Exam 1 Flashcards

Question

Explain dominance (allelic relationship) and complete dominance

Answer 1

Dominance (allelic relationship): - Refers to the expression of one allele over another in a heterozygous genotype - Complete dominance: When the phenotype of the heterozygous genotype is indistinguishable from one of the homozygous genotypes - Example: In pea plants, tall (TT or Tt) is completely dominant over short (tt) - Incomplete dominance: When the heterozygous phenotype is distinct from both homozygous phenotypes - Example: In snapdragons, red (CR) and white (CW) produce pink flowers (CRCw)

Answer 2

When considering a single gene, here are the consequences of segregation, independent assortment, and crossing over: Segregation: - During gamete formation, the two alleles for a gene separate or segregate - This leads to gametes receiving only one allele for that gene - Consequence: Offspring receive one allele from each parent, enabling genetic variation Independent Assortment: - For a single gene, independent assortment does not have an effect - Independent assortment applies when considering two or more genes on different chromosomes Crossing Over: - Crossing over involves the exchange of genetic material between non-sister chromatids of homologous chromosomes - For a single gene, crossing over can result in new combinations of alleles on the same chromosome - Consequence: Increases genetic variation by creating new allele combinations in gametes In summary, for a single gene: - Segregation ensures offspring receive different allele combinations from parents - Crossing over can create new allele combinations on the same chromosome - Independent assortment is not applicable for a single gene

Answer 3

Histone: - Small, highly conserved proteins found in eukaryotic cell nuclei - Act as spools around which DNA winds to form nucleosomes - Help package and order the DNA into structural units called chromatin - Play a role in gene regulation by controlling access to DNA - Core histones: H2A, H2B, H3, H4 form nucleosome core particle - Histone tails can be modified (e.g. acetylation, methylation) affecting gene expression

Answer 4

Nucleosome: - Basic structural unit of chromatin - Consists of a histone core around which DNA is wrapped - Histone core is an octamer of histone proteins (2 copies each of H2A, H2B, H3, H4) - Around 147 base pairs of DNA wrapped around the histone core - Connected by short stretches of linker DNA and linker histones - Allows compaction of DNA into higher-order chromatin structures - Regulates access of enzymes/transcription factors to DNA

Answer 5

Chromatin: - Complex of DNA and proteins that condenses to form chromosomes - Found in the nucleus of eukaryotic cells - Basic unit is the nucleosome (histone core + wrapped DNA) - Allows compaction of long DNA molecules into smaller structures - Exists in two forms: - Euchromatin (less condensed, transcriptionally active) - Heterochromatin (highly condensed, transcriptionally inactive) - Structure and modifications regulate gene expression - Chromatin remodeling alters chromatin structure for DNA access

Answer 6

Uncondensed chromatin refers to loosely packed DNA, allowing for transcription and gene expression. Condensed chromatin is tightly packed DNA, often associated with inactive genes and during cell division.

Answer 7

In genetics, "dominant" refers to an allele that will manifest its phenotype when present, masking the effect of its recessive counterpart in a heterozygous individual.

Answer 8

In genetics, "recessive" refers to an allele whose phenotypic expression is masked by a dominant allele when present in a heterozygous individual. It typically manifests its phenotype only when present in a homozygous recessive genotype.

Answer 9

The "phenotype" refers to the observable traits or characteristics of an organism, resulting from the interaction of its genetic makeup (genotype) with the environment. These traits can include physical features, biochemical properties, and behaviors.

Answer 10

The "genotype" refers to the genetic makeup of an organism, including the combination of alleles present at specific loci on its chromosomes. It represents the genetic information that determines an organism's traits and characteristics.

Answer 11

"Homozygous" refers to an individual having identical alleles at a particular gene locus on both homologous chromosomes. In other words, both alleles at a specific gene locus are the same (e.g., AA or aa).

Answer 12

"Heterozygous" refers to an individual having different alleles at a particular gene locus on homologous chromosomes. In other words, the alleles at a specific gene locus are different (e.g., Aa).

Answer 13

The "law of segregation" is a principle in genetics formulated by Gregor Mendel. It states that during the formation of gametes (sex cells), the two alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. This segregation occurs randomly and independently of alleles at other gene loci.

Answer 14

"Crossing over" is a genetic process that occurs during meiosis, specifically during prophase I of meiosis I. It involves the exchange of genetic material between homologous chromosomes, resulting in the recombination of alleles. Crossing over increases genetic diversity by creating new combinations of alleles on chromosomes.

Answer 15

Allelic relationship, specifically dominance, refers to the interaction between alleles of a gene when present in a heterozygous individual. In a dominant-recessive allelic relationship, the dominant allele expresses its phenotype, masking the effect of the recessive allele. The dominant allele is fully expressed, while the recessive allele's phenotype is only observed when present in a homozygous recessive state.

Answer 16

Complete dominance: Phenotype of heterozygote identical to homozygous dominant.

Answer 17

Sister chromatids: Identical copies of a single chromosome resulting from DNA replication. Homologous chromosomes: Chromosome pairs from each parent, similar in length and gene position but may carry different alleles. To differentiate: - Sister chromatids are identical copies. - Homologous chromosomes are from different parents and may have different alleles. During meiosis: - Sister chromatids are present in both meiosis I and meiosis II. - Homologous chromosomes pair up only in meiosis I.

Answer 18

Interphase: DNA exists as chromatin, loosely packed for gene expression and replication.M phase: DNA condenses into visible chromosomes for accurate segregation during cell division.

Answer 19

Mendelian gene rules: 1. Law of Segregation: During gamete formation, the two alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. 2. Law of Independent Assortment: Alleles for different genes segregate independently of each other during gamete formation. Complete dominance definition: Complete dominance occurs when the phenotype of the heterozygous genotype is indistinguishable from that of the homozygous dominant genotype. In other words, one allele completely masks the effect of the other allele in a heterozygous individual. The dominant allele is fully expressed, while the recessive allele has no observable effect on the phenotype. Identifying complete dominance: To identify complete dominance, observe the phenotype of heterozygous individuals. If the phenotype of the heterozygote is identical to that of the homozygous dominant individual, complete dominance is occurring. In other words, if there is no visible difference between the heterozygote and the homozygous dominant individual, complete dominance is likely at play.

Answer 20

Crossing over: Exchange of genetic material between homologous chromosomes during meiosis, creating new combinations of alleles for one gene.Independent assortment: Alleles for different genes segregate independently during gamete formation, leading to different combinations of alleles for one gene in gametes.Impact: Increases genetic diversity among gametes by generating new allele combinations, contributing to variability in offspring.

Answer 21

To find genotype or phenotype probabilities: 1. Identify parent genotypes. 2. Use Punnett square to visualize offspring genotypes. 3. Count squares for each genotype. 4. Divide by total squares for genotype probabilities. 5. Adjust for phenotype probabilities based on genotype-phenotype relationship or additional information.

Answer 22

In a monohybrid cross with complete dominance, where one allele completely masks the effect of the other allele, the genotype and phenotype ratios in the offspring are predictable. Genotype ratio: - 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive Phenotype ratio: - 3 individuals showing the dominant phenotype : 1 individual showing the recessive phenotype This ratio follows the Mendelian principles of inheritance, specifically the law of segregation and complete dominance, where the dominant allele masks the expression of the recessive allele in heterozygous individuals.

Answer 23

Genes: DNA segments with instructions for traits. Alleles: Different gene versions. Central Dogma: DNA to RNA to protein flow. Mutation: DNA sequence change.

Answer 24

Genotype to Protein: Genes (genotype) encode instructions for protein synthesis. Through transcription and translation, mRNA is produced and translated into proteins.Protein Function: Proteins perform various functions in the cell, such as enzymatic activity, structural support, or signaling. The specific function of a protein determines the phenotype.Biallelic Expression: In biallelic expression, both alleles contribute to the phenotype. If one allele is mutated (e.g., LOF or GOF), it affects protein function and thus the phenotype.Loss of Function (LOF) Mutants: LOF mutations result in a protein with reduced or abolished function. This can occur through various mechanisms such as premature stop codons, altered protein folding, or disrupted binding sites. As a result, the phenotype may show a loss or reduction of the protein's normal function.Gain of Function (GOF) Mutants: GOF mutations lead to a protein with new or enhanced functions. This can arise from mutations that increase protein activity, alter protein interactions, or confer novel properties. GOF mutations can result in abnormal phenotypes due to the altered protein function.

Answer 25

A monohybrid refers to a genetic cross involving only one trait, typically governed by one gene with two different alleles. In a monohybrid cross, individuals with different alleles for the same gene are crossed to study the inheritance pattern of that specific trait.

Answer 26

"Mutant" and "variant" are terms used in genetics to describe alterations or differences in the DNA sequence compared to a reference or wild-type sequence. - **Mutant**: A mutant refers to an organism or cell with a genetic mutation, which is a permanent change in the DNA sequence. Mutations can arise spontaneously or be induced by external factors like radiation or chemicals. Mutations can result in changes to an organism's traits or characteristics. - **Variant**: A variant refers to a version or form of a gene or DNA sequence that differs from the reference or wild-type sequence found in most individuals of a species. Variants can be natural variations within a population or population-specific differences. Variants may or may not have a discernible effect on phenotype, and they can be benign or pathogenic depending on their impact on protein function or gene regulation.

Answer 27

A silent mutation is a DNA change that doesn't alter the amino acid sequence of a protein.

Answer 28

A missense mutation is a type of mutation that occurs in a DNA sequence, resulting in the substitution of one amino acid for another in the corresponding protein. Unlike silent mutations, which do not change the amino acid sequence, missense mutations lead to the production of a protein with a different amino acid at one position. Depending on the specific amino acid change and its location within the protein, missense mutations can have varying effects on protein structure and function. They can range from being benign with little or no effect to causing significant alterations in protein activity or stability, potentially leading to changes in the phenotype of the organism.

Answer 29

A nonsense mutation is a type of mutation that occurs in a DNA sequence, resulting in the premature termination of protein synthesis. This happens when a codon that normally codes for an amino acid is changed to a stop codon (e.g., UAA, UAG, or UGA). As a result, translation of the mRNA molecule is terminated prematurely, leading to the production of a truncated, nonfunctional protein. Nonsense mutations often result in loss of protein function and can lead to genetic disorders or diseases, depending on the specific gene affected and its role in cellular processes.

Answer 30

Determining complete vs. incomplete vs. co-dominance involves understanding how alleles interact: - Complete dominance: Only the dominant allele's phenotype matters. - Incomplete dominance: Phenotype is a blend of both alleles. - Co-dominance: Both alleles' phenotypes are expressed equally.

Answer 31

In incomplete dominance and co-dominance: - Incomplete: Heterozygotes show an intermediate phenotype, suggesting partial protein function from both alleles. - Co-dominance: Heterozygotes express both alleles fully, indicating separate and simultaneous protein functions.

Answer 32

Multiple allelism: Presence of more than two alleles for a gene. Results in varied dominance rules due to specific interactions between alleles.

Answer 33

Autosomes vs. Sex Chromosomes: - Autosomes: Non-sex determining chromosomes (pairs 1 to 22). - Sex Chromosomes: Determine an individual's sex (X and Y in humans). Autosomal Genes vs. Sex-linked Genes: - Autosomal Genes: Located on autosomes, follow Mendelian inheritance. - Sex-linked Genes: Located on sex chromosomes, show different inheritance patterns between males and females.

Answer 34

Pleiotropy is a phenomenon in genetics where a single gene affects multiple, seemingly unrelated phenotypic traits. In other words, a mutation in one gene can lead to the expression of multiple phenotypic characteristics, which may appear unrelated at first glance. This can occur because genes often code for proteins with multiple functions or are involved in multiple biochemical pathways within the cell. Pleiotropy can have significant implications for the understanding of genetic disorders and the development of traits in organisms.

Answer 35

Multiple allelism: Presence of more than two allelic forms of a gene in a population.

Answer 36

Sex-linked gene: Gene located on the sex chromosomes, exhibiting different inheritance patterns between males and females.

Answer 37

Pseudoautosomal regions (PARs) are specific regions of the X and Y chromosomes that share homologous sequences and undergo recombination during meiosis. These regions are termed "pseudoautosomal" because they behave like autosomes in terms of recombination, despite being located on sex chromosomes. PARs are essential for the proper pairing and segregation of the X and Y chromosomes during meiosis, ensuring accurate transmission of genetic information. Recombination in PARs allows for the exchange of genetic material between the X and Y chromosomes, contributing to genetic diversity.

Answer 38

Pleiotropy refers to a genetic phenomenon where a single gene influences multiple, seemingly unrelated traits or phenotypes. In other words, a mutation in a single gene can have effects on multiple aspects of an organism's phenotype. This can occur because genes often play roles in multiple biochemical pathways or have diverse functions within cells or organisms. Pleiotropy is an important concept in genetics and can have significant implications for understanding the genetic basis of complex traits and diseases.

Answer 39

In incomplete dominance and co-dominance: - Incomplete: Heterozygotes show partial protein function, leading to an intermediate phenotype. - Co-dominance: Both alleles produce functional proteins with distinct properties, resulting in simultaneous expression of both phenotypes.

Answer 40

In multiple allelism: - Complete dominance: One allele fully masks others. - Incomplete dominance: Alleles blend in heterozygotes. - Co-dominance: Multiple alleles are equally dominant, fully expressed.

Answer 41

- **Sex-linked genes** are located on the sex chromosomes, X and Y. - In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). - To determine if a gene is sex-linked, examine the inheritance pattern in offspring. Look for differences in ratios between males and females. - If a gene is located on the X chromosome and shows a different inheritance pattern in males and females, it is likely sex-linked. - Inheritance patterns of sex-linked genes often result in different ratios between males and females in a population. - For example, in X-linked recessive traits, males are more commonly affected because they have only one X chromosome. Females need two copies of the recessive allele to express the trait. - Conversely, X-linked dominant traits may affect both males and females, but males often show more severe symptoms since they only have one X chromosome. - Y-linked traits are passed from fathers to sons and are typically rare because the Y chromosome is much smaller and carries fewer genes compared to the X chromosome. - Analyzing pedigree charts and observing the pattern of inheritance across generations can also help determine if a gene is sex-linked. - Genetic testing and molecular techniques can provide definitive evidence of whether a gene is sex-linked by identifying its location on the sex chromosomes.

Answer 42

- **Independent assortment** is a principle of genetics stating that alleles of different genes segregate independently during the formation of gametes. - When considering two genes located on different chromosomes, their alleles assort independently of each other during gamete formation. - This means that the inheritance of one gene does not influence the inheritance of the other gene. - During meiosis, homologous chromosomes segregate independently into daughter cells, resulting in a random assortment of alleles from different genes into gametes. - The number of possible gamete combinations is determined by the number of chromosome pairs undergoing independent assortment. - For example, if an individual is heterozygous (AaBb) for two genes located on different chromosomes, independent assortment results in four different gamete combinations: AB, Ab, aB, and ab. - The principle of independent assortment contributes to genetic variation within populations by generating diverse combinations of alleles in gametes. - This process allows for the creation of unique genotypes in offspring, enhancing genetic diversity and adaptability within a population.

Answer 43

1. **Identify the parental genotypes**: Determine the genotypes of the parents for each gene involved in the cross. 2. **Determine the possible gametes**: List all possible gametes that each parent can produce for each gene. 3. **Construct a Punnett square or use probability calculations**: For each gene, create a Punnett square or use probability calculations to determine the genotypic and phenotypic ratios in the offspring. 4. **Combine results for multiple genes**: If there are multiple genes involved, combine the results from each gene to determine the overall frequencies of genotypes and phenotypes in the offspring. 5. **Calculate frequencies**: Count the number of each genotype and phenotype in the offspring and calculate their frequencies by dividing the count by the total number of offspring. 6. **Consider linkage and recombination**: If the genes are on the same chromosome and are linked, consider the possibility of recombination events affecting the genotypic and phenotypic ratios. 7. **Interpret the results**: Analyze the frequencies to determine the expected distribution of genotypes and phenotypes in the offspring population. 8. **Compare with observed data**: Compare the calculated frequencies with observed data from experiments or real-world populations to validate the predictions.

Answer 44

1. **Making Gametes**: - For each parent, determine all possible gametes they can produce based on their genotype. - If the parent is heterozygous (Aa), they can produce two types of gametes, each carrying one allele (A or a). - If the parent is homozygous (AA or aa), they produce only one type of gamete, carrying the same allele. 2. **Punnett Squares**: - Use Punnett squares to predict the genotypic outcomes of offspring from a cross. - Place the possible gametes from one parent along the top of the square and the possible gametes from the other parent along the side. - Fill in the squares with combinations of gametes to determine the genotypes of the offspring. 3. **Probability Rules**: - Apply probability rules to determine the likelihood of each genotype in the offspring. - Use the "and" rule: Multiply the probabilities of independent events to find the probability of both events occurring. - Use the "or" rule: Add the probabilities of mutually exclusive events to find the probability of either event occurring. 4. **Forkline Method**: - The forkline method is a visual representation of the gamete combinations and their probabilities. - Draw lines representing the possible gametes from each parent and label them with the corresponding alleles. - Use branches to show all possible combinations of gametes and calculate the probability of each genotype in the offspring. 5. **Combining Skills**: - Use a combination of making gametes, Punnett squares, probability rules, and the forkline method to calculate frequencies of genotypes and phenotypes in offspring. - Consider the inheritance patterns of each gene and whether they are linked or independent to make accurate predictions. By employing these skills together, you can effectively analyze and predict the outcomes of crosses involving multiple genes and calculate the frequencies of genotypes and phenotypes in the offspring.

Answer 45

**Linked Genes:** - Linked genes are located on the same chromosome. - They don't independently assort during meiosis. **Consequences:** - Linked genes violate Mendel's law of independent assortment. - Offspring often inherit linked genes together, deviating from expected genetic ratios. - This phenomenon, known as genetic linkage, affects genetic diversity and inheritance patterns. - Understanding linked genes is crucial for accurate predictions in genetics.

Answer 46

To calculate the distance between two genes in centimorgans (cM):Perform a cross.Count the number of recombinant offspring.Divide the number of recombinant offspring by the total offspring and multiply by 100.For example, if 20 out of 200 offspring are recombinant, the distance is (20/200)×100=10(20/200) \times 100 = 10(20/200)×100=10 cM.

Answer 47

1. **Understand Cis and Trans Arrangements**: - In a cis arrangement, alleles of two linked genes are on the same chromosome and stay together during meiosis and gamete formation. - In a trans arrangement, alleles of two linked genes are on different chromosomes or are far apart on the same chromosome and can segregate independently during meiosis. 2. **Perform a Test Cross**: - Cross the heterozygous individual (AaBb) with a homozygous recessive individual (aabb). 3. **Analyze the Offspring**: - Examine the phenotypes of the offspring resulting from the test cross. - If the alleles of the two genes are in cis arrangement in the heterozygous parent, the gametes produced will carry either the dominant alleles (AB) or the recessive alleles (ab). - If the alleles are in trans arrangement, the gametes produced will be Ab and aB. 4. **Observe the Progeny Ratios**: - If the linked genes are in cis arrangement in the heterozygous parent, the offspring will exhibit non-parental phenotypes at a low frequency. - If the linked genes are in trans arrangement, the offspring will exhibit non-parental phenotypes at a higher frequency. 5. **Interpret the Results**: - A higher frequency of non-parental phenotypes suggests a trans arrangement, while a lower frequency suggests a cis arrangement. - The ratio of parental to non-parental phenotypes can provide insight into the linkage arrangement of the alleles.

Answer 48

The relative position of genes on chromosomes is determined by the frequency of genetic recombination. Genes that are closer together on a chromosome tend to have lower rates of recombination, while genes further apart exhibit higher rates. This principle, known as genetic linkage, allows researchers to estimate gene distances based on recombination frequencies, providing insights into chromosome structure and inheritance patterns.

Answer 49

A linked gene refers to genes located on the same chromosome, often inherited together due to their physical proximity and tendency to be passed on as a unit during meiosis.

Answer 50

Linkage refers to the tendency of genes located close together on the same chromosome to be inherited together as a unit, rather than independently assorting during meiosis.

Answer 51

A centimorgan (cM) is a unit of measure used to quantify the relative distance between genes on a chromosome based on the frequency of genetic recombination between them during meiosis. It represents a 1% chance of recombination occurring between two loci on average.

Answer 52

A map unit, also known as a centimorgan (cM), is a measurement unit used in genetics to quantify the distance between two genes on a chromosome. One map unit is equivalent to a 1% chance of genetic recombination occurring between two loci during meiosis.

Answer 53

Recombinant frequency, also known as recombination frequency, refers to the proportion of offspring that display new combinations of alleles compared to the parental generation during genetic recombination. It is typically expressed as a percentage or a fraction and is used to estimate the distance between genes on a chromosome.

Answer 54

Here are the key steps to calculate probabilities with mixed rules (e.g. complete dominance for one gene and incomplete dominance for another gene): 1) Assign genotypic symbols for each gene/trait - For complete dominance: Capital letter (A) = dominant, lowercase (a) = recessive - For incomplete dominance: Capital letters represent different alleles (C, c) 2) Determine parental genotypes and gamete formation - Complete dominance: Aa will form A and a gametes - Incomplete dominance: Cc will form C and c gametes 3) Set up a Punnett square combining all possible gamete combinations 4) Fill in genotypes in the Punnett square boxes based on the assigned symbols 5) Identify the phenotypic ratios for each trait based on dominance relationships - Complete: 3:1 ratio if one parent is heterozygous - Incomplete: 1:2:1 ratio if parents are heterozygous 6) Calculate probability by counting genotype numbers and dividing by total This allows you to predict genotypic and phenotypic ratios when working with mixed dominance rules for different genes in a single cross.

Answer 55

Here are the key steps to set up a test cross for linkage, analyze the results, calculate map distance in centiMorgans (cM), and determine if linked alleles are in cis or trans configuration: Setting up a test cross: - Cross an individual with unknown genotype (doubly heterozygous) to a homozygous recessive individual - Example: AaBb x aabb Analyzing results: - If genes are unlinked (on different chromosomes), you'll see 1:1:1:1 ratio of parental types:non-parental types - If genes are linked, the parental types will be more frequent than non-parental types Calculating map distance: - Map distance in cM = (# recombinant offspring / total offspring) x 100 - More recombinants = greater distance between genes on chromosome Determining cis vs trans: - Cis = Linked alleles on the same chromosome - Trans = Linked alleles on different homologous chromosomes - If parental genotypes are more frequent than recombinants, alleles are in cis - If recombinant genotypes are more frequent, alleles are in trans So by setting up a testcross, you can detect linkage, quantify it by map distance, and discern whether linked alleles started on the same or different homologous chromosomes.

Answer 56

Got it, here's an overview of the different gene-to-trait relationships: 1 gene = 1 trait - Classic Mendelian inheritance pattern - One gene controls one phenotypic trait - Example: Pea plant height controlled by one gene (TT or Tt = tall, tt = short) 1 gene = >1 trait (pleiotropy) - One gene influences multiple phenotypic traits - Example: Sickle-cell anemia gene affects red blood cell shape and ability to carry oxygen 2 genes = 2 traits (same as 1 gene = 1 trait) - Each gene controls a different single trait - Traits assorted independently in inheritance 2+ genes = 1 trait (multigene or polygenic traits) - Multiple genes contribute to and influence a single phenotypic trait - Genes have additive effects or interact in complex ways - Example: Human height, skin color influenced by many genes Key Differences: - Multigene traits controlled by several genes, not a single gene - Effects are additive or showing complex interactions - Don't follow simple Mendelian inheritance patterns Understanding these distinctions is important for interpreting trait inheritance patterns beyond just single gene traits.

Answer 57

A quantitative trait is a characteristic influenced by multiple genes, resulting in a wide range of phenotypic variations. It could be something like height or weight in humans. Discrete traits have distinct categories, like eye color (blue, brown, green), while continuous traits exist on a spectrum, like height or weight. So, if the trait can vary across a spectrum rather than falling into distinct categories, it's likely a quantitative trait.

Answer 58

Recessive epistasis occurs when the presence of one gene masks the expression of another gene at a different locus. In this case, the allele of one gene (the epistatic gene) completely suppresses the expression of alleles of another gene (the hypostatic gene). This often results in a 9:3:4 phenotypic ratio in the offspring when two genes are involved in a dihybrid cross. An example would be the coat color in Labrador retrievers, where the presence of a specific allele in one gene masks the expression of alleles in another gene controlling coat color.

Answer 59

Dominant epistasis occurs when the presence of one allele of a gene masks the expression of alleles at a different locus, regardless of whether the allele is dominant or recessive. In other words, the dominant allele of one gene suppresses the expression of alleles of another gene. An example is the coat color in squash plants, where the presence of a dominant allele at one gene locus masks the expression of alleles at another gene locus controlling pigment production.

Answer 60

Complementary gene action occurs when two different genes work together to produce a specific phenotype. In this interaction, both genes need to contribute a functional allele for the trait to be expressed. However, the presence of either gene alone is not sufficient to produce the phenotype. An example is the flower color in sweet peas, where one gene controls the production of pigment and another gene controls the production of an enzyme required for pigment synthesis. Only when both functional alleles are present can the flower exhibit the desired color.

Answer 61

Environmental effects can influence phenotypes in several ways. For example, environmental factors can affect the expression of genes involved in protein production, leading to differences in protein abundance or activity. Additionally, environmental conditions such as temperature, pH, and nutrient availability can directly impact protein folding and function. Even if individuals have the same genotype, differences in their environments can lead to variations in phenotype due to these environmental influences on gene expression and protein function.

Answer 62

A multi-genic trait, also known as a polygenic trait, refers to a characteristic that is controlled by the combined action of multiple genes. These genes often interact in complex ways to produce the phenotype. Traits such as height, weight, skin color, and intelligence are examples of polygenic traits in humans. Unlike traits controlled by a single gene (monogenic traits), polygenic traits exhibit a continuous range of variation rather than distinct categories.

Answer 63

Epistasis is a genetic phenomenon where the expression of one gene masks or modifies the expression of another gene at a different locus. This interaction can result in unexpected phenotypic ratios in offspring. There are different types of epistasis, including dominant and recessive epistasis, where one gene suppresses the expression of another gene's alleles. Epistasis plays a significant role in shaping the inheritance patterns of traits in various organisms.

Answer 64

Multigene traits can present themselves phenotypically in a variety of ways due to the complex interactions between multiple genes. Phenotypes of multigene traits often exhibit continuous variation, meaning they fall along a spectrum rather than distinct categories. This results in a wide range of phenotypic expressions within a population. For example, in the case of human height, multiple genes contribute to the overall height of an individual, leading to a continuous distribution of heights ranging from short to tall. Similarly, traits such as skin color, intelligence, and susceptibility to diseases are influenced by the combined effects of multiple genes and environmental factors, resulting in a spectrum of phenotypic variations.

Answer 65

In the context of identifying dominant and recessive alleles in a non-epistatic gene, it's important to recognize that the non-epistatic gene is the gene whose expression is affected by the epistatic gene. Let's consider a hypothetical scenario where Gene A is the epistatic gene and Gene B is the non-epistatic gene. If Gene A is dominant, it will mask the expression of Gene B. In this case, the dominant allele of Gene A will prevent the expression of the alleles of Gene B. Therefore, the alleles of Gene B that are unaffected by the dominant allele of Gene A will be expressed, and those are the alleles we can identify as dominant or recessive based on their interaction. For example: - If the dominant allele of Gene A is present (AA or Aa), then regardless of the alleles of Gene B, the phenotype controlled by Gene B will not be expressed. - If the recessive allele of Gene A is present (aa), then the phenotype controlled by Gene B will be expressed based on its own dominant and recessive alleles. So, in this scenario, we can identify the dominant and recessive alleles of Gene B based on their expression when Gene A is recessive.

Answer 66

Identifying the epistatic gene involves recognizing which gene's alleles have the overriding influence on the expression of another gene's alleles. In other words, it's the gene whose alleles mask or modify the expression of alleles of another gene at a different locus. To identify the epistatic gene: 1. Look for the gene whose alleles suppress or modify the expression of alleles of another gene. 2. Determine if the presence of certain alleles of this gene alters the expected phenotypic ratio based on Mendelian inheritance patterns. 3. In a genetic cross, observe which gene's alleles dominate in determining the phenotype of the offspring, even when alleles of another gene are present. Once you've identified the gene whose alleles exert this overriding influence, you've found the epistatic gene in the genetic interaction.

Answer 67

Determining the mode of inheritance using a pedigree involves analyzing patterns of inheritance within a family tree. Here's how you can identify different modes of inheritance: 1. **Autosomal Dominant Inheritance:** - In an autosomal dominant pedigree, affected individuals typically have an affected parent. - The trait usually appears in every generation. - Affected individuals have at least one affected parent. - Both males and females are affected with equal frequency. - If one parent is affected (heterozygous), there is a 50% chance of passing the trait to each child. - A vertical pattern of inheritance is observed. 2. **Autosomal Recessive Inheritance:** - In an autosomal recessive pedigree, affected individuals may have unaffected parents. - The trait may skip generations. - Affected individuals often have unaffected parents who are carriers. - Males and females are equally affected. - If both parents are carriers, there is a 25% chance of having an affected child. - Consanguineous (related) matings increase the likelihood of autosomal recessive inheritance. 3. **X-linked Dominant Inheritance:** - In an X-linked dominant pedigree, affected males pass the trait to all their daughters but not to their sons. - Affected females pass the trait to both sons and daughters. - Every affected individual has an affected parent. - There is no male-to-male transmission. - Affected males typically have unaffected fathers and affected mothers (if the mother is affected, all daughters will also be affected). 4. **X-linked Recessive Inheritance:** - In an X-linked recessive pedigree, affected males usually have unaffected parents. - The trait skips generations. - Affected males are usually born to unaffected carrier mothers. - Affected females are usually born to carrier mothers and affected fathers. - All daughters of affected fathers are carriers, but no sons are affected. - Males are more frequently affected than females. By examining these patterns within a pedigree, you can determine the mode of inheritance for a particular trait.

Answer 68

GWAS, or Genome-Wide Association Studies, are research methods used to find genetic variations linked with specific traits or diseases across an entire genome. Researchers collect DNA samples from many individuals, both affected and unaffected, then compare the genetic differences between them to identify associations with the trait or disease being studied. By analyzing millions of genetic markers, researchers can pinpoint regions of the genome associated with the trait or disease. GWAS have been crucial in understanding the genetic basis of various conditions and traits, from diabetes to height.

Answer 69

In GWAS, linkage refers to the tendency of nearby genetic markers (like SNPs) to be inherited together. SNPs close to genes affecting traits are more likely to be inherited with those genes. Crossing over during meiosis can break apart associations between distant SNPs and traits by shuffling genetic material.

Answer 70

The genome refers to the complete set of genetic material (DNA) present in an organism. It includes all the genes, as well as non-coding sequences, within the chromosomes of an organism. The genome contains the instructions for the development, functioning, and reproduction of the organism. In humans, the genome consists of approximately 3 billion base pairs of DNA organized into 23 pairs of chromosomes.

Answer 71

GWAS stands for Genome-Wide Association Studies. These studies analyze genetic variations across the entire genome to identify associations between specific genetic variants (such as SNPs) and traits or diseases. GWAS have been instrumental in understanding the genetic basis of complex traits and diseases, from height and weight to diabetes and cancer. They help researchers pinpoint regions of the genome that may influence particular traits or diseases, offering insights into potential biological mechanisms and targets for further investigation and treatment.

Answer 72

Non-coding DNA refers to regions of the genome that do not contain instructions for producing proteins. While coding DNA contains genes that encode proteins, non-coding DNA does not directly produce proteins but still plays important roles in gene regulation, chromosome structure, and other cellular processes. Non-coding DNA includes regulatory sequences, such as promoters and enhancers, as well as structural elements like telomeres and centromeres. Despite not coding for proteins, non-coding DNA is crucial for the proper functioning and regulation of genes within the genome.

Answer 73

Coding DNA, also known as exons, refers to the regions of the genome that contain the instructions for producing proteins. These sequences are transcribed into messenger RNA (mRNA) during the process of gene expression and are subsequently translated into amino acids, which then form proteins. Coding DNA is characterized by the presence of open reading frames (ORFs) that can be translated into functional protein sequences. Mutations in coding DNA can lead to changes in the amino acid sequence of proteins, potentially altering their structure and function, and contributing to genetic diseases or variations in traits.

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is the number of complete genomes in a cell. We represent this with n, 2n, 3n, 4n, etc

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is the number of chromosomes in one genome

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two complete genomes or two complete sets of chromosomes

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cells in ovaries and testes that create gametes

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sex cells (egg/sperm)

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cells in all other areas of body (arise when zygote grows and develops through mitotic division)

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separate every homologous chromosome – we stick homologs together, align, and separate them

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one duplicate (sister) in each cell – basically mitosis to separate sisters in meiosis II

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Uncondensed chromosomes replicate in parent cell (2n germ cell)

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Nuclear envelope begins to break down * Chromosomes condense * The spindle apparatus begins to form * The homolog pairs come together in a pairing process called synapsis * The structure that results from synapsis is called a bivalent, consisting of two homologs * The chromatids of the homologs are called non-sister chromatids

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* Synaptonemal complex removed * Homologs remain attached at chiasmata * Exchange or crossing over between homologous non-sister chromatids occurs * Produces chromosomes with a combination of maternal and paternal alleles

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* The paired homologs line up at the metaphase plate * Alignment of the homologs is random: maternal and paternal chromosomes can be on either side of the metaphase plate

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* Homologous pairs of chromosomes are separated (break chiasmata) * of each pair one chromosome (consisting of two chromatids) moves to one pole, while the other moves to the other pole

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* the homologs finish migrating to the poles of the cell * Then the cell divides in the process of cytokinesis PLOIDY HAS BEEN REDUCED! (Reductive division)

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Independent Assortment: * In previous example, with just 2 chromosome pairs, we saw the chromosomes could line up in two different ways * This resulted in 22 = 4 different gametes * In humans, 23 pairs of homologous chromosomes * Paternal and maternal chromosomes line up on different sides of the metaphase plate during metaphase I independently * This creates: 223 = 8.4 million possible combinations of maternal and paternal chromosomes

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DNA associated with nucleosomes (histones) is called chromatin

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DNA ”condenses”

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Sister chromatids: Two identical copies of the same chromosome Joined together at the centromere Result from DNA replication during the S phase Separate during anaphase of mitosis or meiosis II Homologous chromosomes: One chromosome from each parent Contain the same genes but may have different versions (alleles) Pair up and exchange genetic material during meiosis I Separate during anaphase I of meiosis

Answer 92

Sisters: Identical banding patterns Same length and centromere position Originate from the same parental pair of homologous chromosomes Homologous chromosomes: Similar banding patterns Same length and centromere position Carry genes for the same traits (one from each parent) Can form a bivalent during meiosis Non-homologous chromosomes: Distinct banding patterns Different lengths and centromere positions Carry genes for different traits Cannot form bivalents during meiosis Clues: Look for similarities in banding patterns, length, and centromere position Chromosomes with identical patterns and features are sisters Chromosomes with similar (but not identical) patterns and features are homologous Chromosomes with distinct patterns and features are non-homologous

Answer 93

Ploidy: Diploid (2n): Cells with two sets of chromosomes (one from each parent) Haploid (n): Cells with a single set of chromosomes Determining 2n or n: Count the number of distinct chromosomes (non-homologous pairs) If there are two copies of each chromosome, it's diploid (2n) If there's only one copy of each chromosome, it's haploid (n) Phase of meiosis that causes 2n to n transition: Meiosis I Specifically, during Anaphase I Homologous chromosomes separate, resulting in two haploid (n) daughter cells Steps: Diploid (2n) cell undergoes meiosis During Metaphase I, homologous chromosomes pair and form bivalents In Anaphase I, homologous chromosomes separate, and each daughter cell receives one chromosome from each homologous pair Two haploid (n) daughter cells are produced after Meiosis I These haploid cells undergo Meiosis II, resulting in a total of four haploid (n) cells

Answer 94

Chromatin: Chromatin is the complex of DNA and proteins (primarily histones) that makes up chromosomes. It exists in two states: condensed and uncondensed. Uncondensed Chromatin: Also known as "euchromatin." The DNA is loosely packaged and extended. It is the more accessible form of chromatin, allowing for transcription and other cellular processes. Uncondensed chromatin is found during interphase (G1, S, and G2 phases) of the cell cycle. Condensed Chromatin: Also known as "heterochromatin." The DNA is tightly packaged and compacted. It is less accessible for transcription and other processes. Condensed chromatin is found during cell division (mitosis and meiosis). During mitosis and meiosis, the chromatin goes through a cycle of condensation and decondensation: Interphase: Chromatin is mostly uncondensed (euchromatin). Prophase: Chromatin begins to condense into visible chromosomes (heterochromatin). Metaphase: Chromatin is highly condensed, and chromosomes are at their most compact state. Anaphase: Chromosomes remain condensed as they separate. Telophase: Chromatin begins to decondense as the nuclear envelope reforms. Interphase: Chromatin returns to its mostly uncondensed state (euchromatin).

Answer 95

Meiosis I: Prophase I: Chromatin condenses into chromosomes Homologous chromosomes pair up and form bivalents (tetrads) Crossing over (genetic recombination) occurs between non-sister chromatids Metaphase I: Bivalents line up at the metaphase plate Anaphase I: Homologous chromosomes separate (leading to a reduction in chromosome number from 2n to n) Sister chromatids remain together Telophase I: Separated chromosomes move to opposite poles Nuclear membranes reform around each haploid set Meiosis II (occurs in both daughter cells): Prophase II: No pairing or crossing over occurs Metaphase II: Chromosomes line up at the metaphase plate Anaphase II: Sister chromatids separate Telophase II: Separated chromatids (now individual chromosomes) move to opposite poles Nuclear membranes form around each haploid set Result is four haploid cells Key events: Meiosis I: Reduction division (2n to n) Crossing over in Prophase I Homologous chromosomes separate in Anaphase I Meiosis II: Equational division Sister chromatids separate in Anaphase II Four haploid cells produced at the end

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is the observable trait/characteristic

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is the combination of alleles an individual possesses for a given gene

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means two of the same alleles for a gene are present

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means two different alleles for a gene are present

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There is _1___ trait controlled by __1___ gene. *There are _2__ possible alleles. There are __3_ possible genotypes. There are _2__ possible phenotypes *There are very few TRULY Mendelian human traits. Even the earwax model is not Mendelian in real life.

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tetrads align randomly and independently of other tetrads

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Homologous chromosomes recombine in prophase I of meiosis.

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Alleles segregate into different gametes by the end of meiosis.

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-In a diploid individual, alleles for a gene exist on homologous chromosomes. -These two alleles separate into different gametes due to Law of Segregation. *When considering only ONE gene, we do not need to think about crossing-over or independent assortment* These two processes still happen! but in terms of that one gene, the possible gametes remain unchanged. However, the gametes formed from crossing over and independent assortment considering ALL chromosomes and genes are unique, we just won’t care until we consider more than one gene. One gene Mendel-Meiosis connection summary 24

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heterozygous

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“and” means multiply probabilities “or” means add probabilities

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is usually the one most typically found in natural populations. Usually functional allele. *meaning of wt sometimes is used to mean “standard” or “unmutated

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* A gene is a sequence of DNA that encodes for a protein. * DNA sequence is transcribed to mRNA * Ribosomes translate mRNA to produce a sequence of amino acids (polypeptide) that fold into a unique protein structure *The function of the protein produces the observable phenotype

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a. a transporter that cannot transport cerumen components out of the cell b. a transporter that cannot fold properly or go to the correct location c. a transporter with a new function; it now transports different substances (all of above are possible)

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Can be due to inability to produce protein like this example or protein lacks ability to perform its activity (e.g. an enzyme that cannot bind its substrate)

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c) Both A and B

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Mutations that result in increased protein activity or that result in completely new protein functions. STAT3 is a signaling protein that should be turned on and off properly for normal immune function. stat3 gain of function mutant is always on. Produces an autoimmune disease phenotype. Which allele do you think would be dominant? a. wild type b. Gain of function mutant allele (correct)

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3. T 4. T 5. 1/2

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IB GOF and i is LOF

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When there are more than two alleles for a gene in the population.

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The small homologous regions on the X and Y chromosome are called Pseudoautosomal Regions (PAR). Genes located outside the PARs on the X or Y chromosome are sex- linked genes

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1. “Given XY born” – means we assume XY born so we do not need to include XY probability. We also modify the denominator (remove the XX). 2. Probability of having an XY and this XY has (with) trait – means need to include chance of XY and chance of disease

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Hemoglobin gene –> Trait 1: malarial resistance, Trait 2: Sickle Cell Anemia, Trait 3: blood cell shape

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9 R_Y_ dominant/dominant 3 R_yy dominant/recessive 3 rrY_ recessive/dominant 1 rryy recessive/recessive

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A. does not affect our gamete possibilities

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Because both genes physically on same chromosome, they are inherited together NOT independently!

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recombination frequency gives us a relative idea of how far apart genes are but does not equate to actual nucleotide distance. recombination frequency is equal to the proportion of recombinant gametes formed.

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recombination frequency between two genes is equal to the proportion of recombinant offspring produced in a testcross

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(centimorgans) are arbitrary units that represent distance of genes in terms of recombinant frequency but not actual nucleotide distance.

Answer 125

* When two genes independently assort – it COULD mean one of two things: 1) two genes are on different chromosomes OR 2) on same chromosome but at least 50cM apart. The two cases are NOT distinguishable in a test cross for linkage nor a dihybrid. * In a test cross for linkage between 2 genes, you can never get >50cM EVEN IF the two genes are actually >50cM apart. So if we get 50cM we know the two genes are AT LEAST 50cM apart and independently assort. * In a heterozygous parent for 2 linked genes, the arrangement of alleles in the parent can be in cis or trans. Cis means the dominant alleles are together on one chromosome and the recessive are together on the other. Trans means that one dominant and one recessive allele are together on each chromosome. * The way you tell cis vs. trans is find the big numbers in the test cross result. These must come from the parental chromosomes (without crossing over). So these directly tell us which alleles were together on the parental chromosomes

Answer 126

multi-genic and produces continuous phenotypes. *Usually many more than 2 genes

Answer 127

is when two genes interact to produce one trait and the alleles of one gene mask the other gene. *Epistasis is about GENE relationships Our genes in epistasis will independently assort We will not do crosses with quantitative traits. Be able to recognize.

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homozygous recessive “stands over” other gene

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The dominant allele of one gene masks the phenotype of another gene

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when two different genes work together to contribute to one single trait

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2 genes = 1 discrete trait Epistasis is about non-allelic relationship aka gene relationships (gene interactions). In CONTRAST, allelic relationship, is dominance/incomplete/co relationship between alleles for one gene. The gene that masks the other is called the epistatic gene. So if gene A is masking B we say Gene A is epistatic to Gene B. In epistasis problems the two genes will always ind. assort. We use a dihybrid cross to determine epistasis. You should know the 3 types of epistasis, how their ratios deviate, and how the ratio us which type of epistasis is occurring. PS3 has practice

Answer 132

Variation in a single nucleotide at a particular position in the genome

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No, single nucleotide polymorphisms (SNPs) don't have to occur within a gene. They can also occur in noncoding regions of DNA, most commonly between genes.

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a heterozygote's phenotype

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One of the two phenotypes must be dominant while the other phenotype is recessive.

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The wild type and the mutant alleles will be transcribed and translated.

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produce a mutant protein that has no function at all. produce a mutant protein that has a new function different than wild type function. cause the mutant allele to be dominant over wild type. cause the mutant allele to be recessive to wild type.

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Law of Segregation

Answer 139

What genotype(s) gives the silver phenotype aaB_ and aabb ? What genotype(s) gives the gold phenotype A_B_ ? What genotype(s) gives the iridescent phenotype A_bb ? What phenotypic ratio would we expect in a dihybrid cross 9:3:4 ? What type of gene interaction is occurring recessive epistasis ?

Answer 140

quantitative trait

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environmental interactions

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1. What type of epistasis is occurring? dominant epistasis 2. Which statement is TRUE? quiet allele is dominant over growly allele

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Answer 1: Correct! b Answer 2: Correct! 0 Answer 3: Correct! 1

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Answer 1: Correct! Yes linked Answer 2: Correct! [(100+150)/(1000+1000+100+150)]*100 Answer 3: Correct! True Answer 4: Correct! False

Answer 145

co-dominance

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II. Both parents were heterozygotes. One parent is homozygous and one parent is heterozygous. IV. Toothed is dominant phenotype.

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A. The function of the protein produced by alleles. B. The dominance rules controlling the gene’s alleles. C. The relationship between the alleles of the gene

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11. Assume you discover the disease allele is dominant. Which of the following could be true? A. The disease allele is a loss of function allele. B. The disease allele is a gain of function allele. (Both)

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A. Alleles for the same gene would be inherited together. B. Alleles for the same gene would never separate into distinct gametes

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does produce unique gametes when considering all genes on all chromosomes does not produce unique gametes when considering just one gene of interest

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Fox fur color alleles exhibit incomplete dominance. The parental foxes are heterozygotes.

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b. The alleles for gene X follow complete dominance.

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c. incomplete dominance

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c. pleiotropic (1 gene = multiple traits)

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b. environmental interactions

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c. There are multiple genes controlling the trait.

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A) Is gene interaction occurring? If so, what type of gene interaction is occurring? Yes, dominant epistasis b/c 12:3:1 dihybrid phenotype ratio B) What genotypes will give each phenotype? 9 A_B_ albino 3 A_bb albino 3 aaB_black 1 aabb brown The gene producing albino is epistatic to the gene producing pigment Black allele is dominant over brown allele

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