Genetics Flashcards
(123 cards)
1
Q
DNA Structure Overview
A
Polymer composed of nucleotides
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Q
3 Components of DNA
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Phosphate group, ribose sugar, nitrogenous base
3
Q
The bond between sugar molecule and the phosphate group
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Phosphodiester bond
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Q
Formation of the Phosphodiester Bond
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A condensation reaction in which a ribose sugar loses a hydroxide molecule and a phosphate group loses a hydrogen atom. An excess water molecule forms.
5
Q
Ribonucleotide vs deoxyribonucleotide
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Ribonucleotides have one more oxygen atom than deoxyribonucleotides on the pentose sugar
6
Q
Types of Nitrogenous Bases
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Purines: adenine and guanine, have two smaller rings
Pyrimidines: thymine and cytosine, haev lone, larger rings
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Q
Uracil
A
Replaces thymine in RNA
8
Q
Nucleoside
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Single pentose sugar
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Q
Nucleoside mono/di/…phosphate
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Pentose sugar + one/two/…phosphate groups
10
Q
Chargaff’s Rule
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Adenine pairs with thymine; guanine pairs with cytosine
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Q
Explanation for Chargaff’s Rule
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The location of hydrogen bonds create an energetically stable arrangement: purine to pyrimidine
12
Q
Structure of DNA strands
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Double helical. Double stranded and antiparallel: one 5’ to 3’, other 3’ to 5’.
13
Q
Rosalind Franklin and DNA
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Used X ray crystallography; shot X rays at DNA, scattering and creating a pattern on a plate, creating an image. Discovered that DNA forms a helix, is double stranded, with phosphate molecules stick out.
14
Q
Watson and Crick
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Used Franklin’s work to discover the double helix structure, suggesting possible mechanisms for replication
15
Q
Nucleic Acids
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Categorized as nucleotides, compoased of C, H2, O2, N2 and P, can be DNA, RNA, ATP, coenzymes, responsible for forming genetic materials, energy carriers and enzyme assistants.
16
Q
DNA Replication
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- Helicase disrupts hydrogen bonds long enough to unzip the strands, creating the replication fork. It moves along the strand until complete separation
- Single strand binding proteins prevent reannealation. and come off once they’re no longer needed
- The toposiomerase/gyrase releases torsional tension ahead of the replication fork to release torsional tension
- DNA polymerase builds the new strand of DNA by catalyzing the production of phosphodiester bonds
- A nucleoside triphosphate comes in; the bond between 2 phosphates broken, releasing energy, gets transferred to make the bond between a P group and a carbon from another nucleotide -> monophosphate
- DNA Pol III links the nucleotides in the leading strand with phosphodiester bonds
- As more is built, more is unzipped
- For the lagging strand, DNA Pol III cannot build from 3’ to 5’, so it moves away from the fork, builds, then leaps back to strart with a new segment
- The primse builds RNA 10 nucleotides long, becoming the foundation (primer), needed by both the leading and lagging strand
- DNA Pol I recognizes where the RNA is and replaces it with DNA
- Ligase binds the Okazaki fragments together, creating phosphodiester bonds, creating one continuous strand
17
Q
Goal of Meiosis
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Create haploid cells (gametes) that can be used for sexual reproduction
18
Q
Fertilization
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Two gametes, a sperm and an ovum, each contain the haploid number of chromosomes, fuse together to form a diploid cell
19
Q
Loci
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Location (on a chromosome). A particular spot where protein codes for specific trait: type of info at the same spot.
20
Q
Tetrads (Bivalents)
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Two pairs of homologous chromosomes. Sister chromatids of homologous chromosomes that line up next to each other and temporarily attach, exchanging different segments of their genetic material to form unique recombinant chromosomes
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Q
Chiasma
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Location of crossing over
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Q
Allele
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Alternate version of a gene
23
Q
Maternal and paternal chromosomes in a homologous pair have the same x at the same y but not necessarily the same z
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X: genes
Y: loci
Z: alleles
24
Q
Meiosis I
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Prophase I: chromosomes condense, the nuclear envelope dissolve, crossing over takes place
Metaphase I: tetrads move to the equator of the cell
Anaphase I: homologous chromosomes are pulled to the opposite poles of the cell
Telophase I: chromosomes gather at the poles, the cytoplasm divides
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Meiosis II
Prophase II: a new spindle forms around the chromosomes
Metaphase II: chromosomes line up vertically
Anaphase II: centromeres divide, chromatids move to opposite poles
Telophase II: a nuclear envelope forms around each set of chromosomes, the cytoplasm divides
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Is the cell diploid or haploid during meiosis?
Diploid until telophase I, haploid afterwards.
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Human Karyotype
Image of a person's complete set of chromosomes, can reveal abnormalities
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Non - disjunction
The failure of homologous chromosome pairs to separate properly during meiosis or mitosis, resulting in an imbalance of chromosomes
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Is non - disjunction more destructive during anaphase I or II?
Anaphase I, because four daughter cells are affected instead of two
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Monosomy
Daughter cell missing single chromosome
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Trisomy
Daughter cell has one extra chromosome
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Down Syndrome
Trisomy 21
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Transcription Summary
DNA to RNA synthesis. DNA is copied into single stranded RNA, which is transported into the cytoplasm
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4 Stages of Transcription
1. Initiation
2. Elongation
3. Termination
4. Post - Transcriptional Modifications
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Nontemplate Strand
Coding, sense
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Template
Noncodng, transcribed, antisense
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The promoter
Example of non - coding DNA with a function, located upstream of the gene coding region. "A"s and "T"s in the promoter region serve as a recognition site for RNA polymerase
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Enhancers and Repressors
Upstream from the gene, help determine transcription rate
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The RNA transcript is complementary to the template/nontemplate strand?
Template
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The promoter is upstream/downstream from RNA - coding region?
Upstream
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Transcription Initiation (2 Steps)
1. Enzyme RNA polymerase binds to a strand of DNA to form an initiation complex and opens the doublie helix to form the transcription bubble
2. The binding occurs at a promoter, with a characteristic base pair patter, the TATA box
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Transcription Elongation (3 Steps)
1. RNA polymerase builds RNA from 5' to 3' using nucleoside triphosphates
2. Results in a primary transcript
3. DNA strands reform a helix afterwards
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First Step in Transcription Termination
RNA Pol recognizes the end when it comes across a terminator sequence.
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Eukaryotic Transcription Termination
Terminator sequence is a string of adenines: AAAAAAA
The precursor mRNA, the primary transcript, isn't the full gene yet, as it's vulnerable to enzymes and conditions outside the nucleus and contains non - coding regions
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Prokaryotic Transcription Termination
Two types of terminators: protein binding and stopping transcription or mRNA binding to itself, the complementary bases attracting each other. Then, the mRNA is immediately ready to be translated.
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Post - Transcriptional Modifications
The spliceosome cleaves the intron
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Poly(A) tail
A chain of adenine nucleotides to protect the chain from enzymes in the cytosol
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5' cap
7 sequences of Gs recognized by ribosomes
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Exon
Sequence that codes for part of a gene
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Intron
Non - coding sequence
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Spliceosome
Enzyme - protein complex that removes introns
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Small Nuclear Ribonucleoproteins (snRNO)
Remove the intron without cutting any nucleotides from the exon
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Alternative Splicing
Allows for one gene to code for more than one protein. How the RNA is edited determines the type fo protein created. Introns allow for one gene to code for multiple proteins.
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Translation Function
RNA to protein synthesis
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The Anticodon
A sequence of three bases complementary to the mRNA codon
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The Acceptor Site
On the opposite arm of the anticodon, binds to and carries the corresponding amino acid, has the nucleotide sequence CCA
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Four Stages of Translation
Initiation, elongation, translocation and termination
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A site (Amino acid site)
Position where the new tRNA codon - anticodon binds making sure that the correct AA is in position
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P site (polypeptide site)
Position in which the AA on the tRNA adds to the polypeptide
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Exit site
Position the tRNA, without the AA, locates and is released from the ribosome to become re - activated
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Translation Initiation (5 Steps)
1. Ribosomes bind to the mRNA, recognizing the 5' cap in eukaryotes
2. The tRNA charged with AA methionine has the anti - codon UAC, complementray to the start codon of mRNA, AUG
3. The small subunit associates with the methionine tRNA, moves over start codon
4. The large subunit of the ribosome moves over the mRNA
5. The sart codon occupies the P site, while the A site is free for the complementary tRNA to bind
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Translation Elongation (3 Steps)
1. tRNA enters the A site using the matching of the codon to the anticodon to ensure the correct AA is added
2. Bond between the tRNA and methionine is broken
3. Free energy is released, used to form the peptide bond between methionine and the new AA
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Translation Translocation (3 Steps)
1. The large subunit moves 3 bases towards the 3' end of the mRNA
2. The tRNA for methionine, called methione, enters the E site to exit and become recharged with another mehtionine
3. The elongation process is repeated until termination
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Translation Termination (2 Steps)
1. Stop codons (UAG, UAA, UGA) recognized by the release factor and aids the release of the polypeptide chain from the ribosome
2. 2 subunits of the ribosome fall off the mRNA and separate
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Nucleosome
A molecule of DNA wrapped around a core of eight histone proteins, an octamer
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Octamer
Contain 2 copies of 4 different types of histones
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The ... charged DNA associates with ... charged AA on the surface of the histones
Negatively, positively
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Chromosomal Condensation
Tails that extrude outwards from adjacent octamers link up and draw the nucleosomes together
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Purpose of Nucleosomes
Supercoil DNA for more efficient storage and to protect it from damage and allow chromosomes to be mobile during mitosis and meiosis
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Tightness of Nucleosomes and Transcription Rate
Loosening the nucleosomes increases transcription rate
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Methylation
Addition of methyl groups to DNA: causes nucleosomes to pack tightly together. Transcription factors cannot bind to the DNA and genes are not expressed
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Acetylation
Addition of acetyl groups; results in loose packing, allowing transcription factors to bind.
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Heterochromatin
Tightly packed chromatin
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Euchromatin
Loosely packed chromatin
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Epigenetic Tag
Markers from methylation and acetylation on the DNA that affect transcription
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For a new organism to grow it needs ... DNA that can develop into lots of different specialized cell types
Unmarked
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Factors affecting methylation and acetylation
Changes in the environment, e.g. mother's diet, exercise, which affect the cell metabolism
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Operator
Region of DNA that can regulate transcription, typically inhhibiting transcription
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Enhancer
Non - coding DNA region that increasese transcription rate when an activator protein is bound to it
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Silencer
Non - coding DNA region that inhibit transcription when a repressor protein is bound to it
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Point Mutation
One nucleotide substituted for another
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Sickle Cell Anemia
Example of point mutation: caused by a single substitution error. Adenine substituted by thymine; originally codes for glutamine instead of valine. The cell becomes sickled, crescent shaped, which form clumped hemoglobin that obstruct blood vessels. However, this is beneficial in malaria ridden areas, as paraites are killed by this type of blood.
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Gene Mutation
Change in the nucleotide sequence of a section of DNA
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Mutagen
Agents that cause gene mutations, result in the creation of new alleles
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Examples of Mutagens
Environmental factors like UV and X rays, chemicals like benzene
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Consequences of Radiation
High energy radiation causes mutation in the form of waves or particles that disrupt the backbone of DNA molecules
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Nature of the Impact of Radiation
Duration and intensity
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Non ionizing vs ionizing radiation
Non ionizing radiation has low energy while ionizing radiation has higher energy. Capable of breaking bonds between atoms, anything above UV< alpha and beta particle radiation.
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Gregor Mendel
First documented scientist to conduct a controlled experiment, father of genetics, discovered the principle of dominance
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Principle of Dominance
When organisms with contrasting traits are crossed, the offspring will only display the dominant trait
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Genotype
Specific allelic combination
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Phenotype
Physical appearance of a trait
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Dominance
The allele that's expressed under all circumstances
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Recessiveness
The allele that's masked in the presence of a dominant trait and only expressed in their absence
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Homozygous
The alleles are both dominant or recessive
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Heterozygous
One dominant allele, one recessive
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F1
First filial, first generation of offspring
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F2
Second filial, second generation of offspring
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Monohybdrid Cross
Crossing two organisms with homozygous (pure breeding) genotypes
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Dihybrid Cross
Crossing two heterozygous organisms: two separate monohybrid crosses
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Law of Segregation
Because homologous chromosomes are oriented randomly during metaphase I, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
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Law of Independent Assortment
The alleles of two or more different genes get sorted into gametes independently of one another
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An Exception to Mendel Genetics
Blood type
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Type O Blood
Genotype: ii
Both A and B antibodies present, no antigens
Can only receive from O
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Type A Blood
Genotype: IAIA or IAi
Only antibody B present, only antigen A present
Can receive from O and A
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Type B Blood
Genotype: IBIB or IBi
Only antibody A present, only antigen B present
Can receive from O and B
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Type AB Blood
Genotype: IAIB
No antibodies present, both antigens A and B
Can receive from any blood type
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2 Types of Non - Mendelian Genetics
Incomplete dominance and codominance
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Incomplete Dominance
Two different alleles both partially expressed, blended. No dominance or recessiveness but heterozygous
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Codominance
Two different alleles both fully expressed.
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Sex Linked Traits
Located on chromosome 23
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Y Linked Traits
Only males carry the trait. Rarer than X linked as the Y chromosome is smaller. Leads to male infertility and not passed on, but there are some exceptions. No dominance or recessiveness since there is only one Y chromosome. When drawing a punnett square, signal Y' for having the trait.
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X Linked Traits
Recessive. Female may be carrier but 0% chance get sick. X comes from mother, Y comes from father. For the female offspring to get sick, the motehr has to be a carrier and the father has it.
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Size of X and Y chromosomes
X is larger than Y
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Examples of Sex Linked Syndromes
Hemophilia (X recessive), hairy ears (Y linked)
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Autosomal Traits
On chromosome 1 - 22; not sex linked
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Examples of Autosomal Syndromes
Cystic fibrosis: recessive, excessive mucus production, difficulty breathing and increases infection possibility.
Huntington's Disease: dominant, loss of muscle coordination and cognitive decline
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Pedigree Legend
- Circle for female, square for male
- Horizontal line indicates mating
- Vertical line indicates offspring
- Roman numerals indicate generations
- Shaded has the trait
- Triangle: identical twins
- Cherry shape: fraternal twins
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Continuous vs Discontinuous Variation
Continuous variation occurs when an array of possible phenotypes can be produced. Discontinuous variation cocurs when only a small number of phenotypes can be produced.
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Polygenic Traits
Two or more genes influence the expression of one trait
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Assumptions of Polygenic Traits
1. Each contributing gene has a small and relatively equal effect
2. The effects of each allele are cumulative
3. The value of the trait depends solely on genetics, ignoring environmental influences
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Linked Genes
The tendency of certain genes to be inherited together
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Linked Genes Process
Loci on the samm chromosome that are physically close to one anotehr tend to stay together during meiosis and become linked, resulting in crossing over. No longer independently sorted, not segregated, creates recombinant genotypes.
