3A4 Genetics and Protein Synthesis Flashcards
Explain how DNA and RNA structure and function underlie genetic inheritance, patterns, variability, and disorders.
What does DNA stand for?
Deoxyribonucleic acid
DNA is a molecule that carries genetic instructions for the development, functioning, growth, and reproduction of all known living organisms.
What does RNA stand for?
Ribonucleic acid
RNA plays a role in protein synthesis and can act as genetic material in some viruses.
What is the shape of the DNA molecule?
Double helix
DNA’s double-helix structure was discovered by James Watson and Francis Crick, supported by Rosalind Franklin’s X-ray diffraction data.
What sugar is found in DNA?
Deoxyribose
Deoxyribose is a 5-carbon sugar that lacks an oxygen atom at the 2’ position, distinguishing it from ribose in RNA.
What are the four nitrogenous bases in DNA?
- Adenine
- Thymine
- Cytosine
- Guanine
Adenine pairs with thymine, and cytosine pairs with guanine through complementary base pairing.
True or False:
Thymine is found in RNA.
False
Thymine is found only in DNA, whereas RNA contains uracil instead.
What are the building blocks of DNA?
Nucleotides
Each nucleotide consists of a phosphate group, deoxyribose sugar, and a nitrogenous base.
Fill in the blank:
In DNA, adenine pairs with _________.
Thymine
Adenine pairs with thymine through two hydrogen bonds, maintaining the double-helix structure.
What is the function of DNA?
Storing genetic information.
DNA serves as the blueprint for all cellular processes and is passed from parent to offspring.
Which base is unique to RNA?
Uracil
Uracil replaces thymine in RNA and pairs with adenine during base pairing.
True or False:
RNA is double-stranded like DNA.
False
RNA is typically single-stranded, although it can fold into complex shapes for specific functions.
What are the three types of RNA?
- mRNA
- tRNA
- rRNA
mRNA carries genetic code, tRNA brings amino acids, and rRNA forms ribosomes.
Fill in the blank:
DNA replication occurs in the ________ of eukaryotic cells.
nucleus
DNA replication takes place during the S-phase of the cell cycle in the nucleus.
What is the function of mRNA?
Carrying the genetic code for protein synthesis.
Messenger RNA (mRNA) transfers genetic information from DNA to ribosomes for translation.
What is transcription?
The process of creating RNA from a DNA template.
This occurs in the nucleus where RNA polymerase synthesizes messenger RNA (mRNA).
Fill in the blank:
During translation, amino acids are brought to the ribosome by _______.
tRNA
(transfer RNA)
tRNA contains anticodons that pair with mRNA codons, allowing amino acids to assemble into proteins.
What is the central dogma of molecular biology?
DNA → RNA → Protein
The central dogma explains the flow of genetic information: DNA is transcribed into RNA, which is then translated into proteins.
Where does transcription occur in eukaryotic cells?
In the nucleus.
In eukaryotes, DNA is located in the nucleus, so transcription must occur there.
What enzyme catalyzes transcription?
RNA polymerase
This enzyme binds to the DNA template strand and synthesizes complementary RNA.
True or False:
Transcription occurs in the cytoplasm of prokaryotes.
True
In prokaryotes, transcription occurs in the cytoplasm because they lack a nucleus.
Fill in the blank:
RNA polymerase binds to the ______ during transcription initiation.
promoter
The promoter is a DNA sequence that signals the start of transcription.
Define:
codon
A sequence of 3 nucleotides that code for a specific amino acid.
Also referred to as triplet code, these sequences exist in both DNA and RNA.
For example, the codon “CAG” codes for the synthesis of the amino acid glutamine.
What is the start codon in mRNA?
AUG
AUG codes for the amino acid methionine, and signals the beginning of translation.
What molecule provides energy for translation?
GTP
(Guanosine triphosphate)
GTP provides energy for various steps in the translation process, such as tRNA binding and ribosome movement.
Why is the central dogma important?
It explains how genetic information leads to protein synthesis.
The central dogma outlines the essential flow of information needed for gene expression and protein production.
What are chromosomes?
Structures made of DNA and proteins that carry genetic information.
Chromosomes are found in the nucleus of eukaryotic cells and contain genes that determine traits.
How many chromosomes do humans have in each somatic cell?
46 chromosomes (23 pairs)
Humans inherit 23 chromosomes from each parent, resulting in 23 pairs of homologous chromosomes.
Define:
Gene
A segment of DNA that codes for a specific protein or trait.
They are the basic units of heredity and determine specific characteristics, such as eye color or blood type.
What are the three main stages of transcription?
- Initiation
- Elongation
- Termination
Initiation begins the process, elongation builds the RNA strand, and termination ends transcription.
Where are genes located?
On chromosomes.
Genes occupy specific positions called loci on chromosomes. Each gene carries instructions for a trait.
True or False:
All chromosomes are identical in structure and function.
False
Chromosomes vary in size, shape, and the genetic information they carry. Autosomes and sex chromosomes have different roles.
What is an allele?
A variant form of a gene.
Alleles are different versions of the same gene that can result in variations in a trait, such as blue or brown eyes.
Generally, how many alleles for a gene does an individual inherit?
Two—one from each parent.
For most traits, individuals inherit one allele from the mother and one from the father.
Fill in the blank:
Chromosomes are made up of _____ and proteins.
DNA
Chromosomes consist of tightly packed DNA molecules wrapped around proteins called histones.
What are sex chromosomes?
Chromosomes that determine the biological sex of an organism.
Humans have two sex chromosomes—XX in females and XY in males.
There are some genetic conditions where people inherit more than two sex chromosomes, such as Klinfelter (XXY) and Triple X Syndrome (XXX).
What is genotype?
The genetic makeup of an organism.
Genotype refers to the combination of alleles (e.g., AA, Aa, or aa) inherited from both parents that determine an organism’s traits.
Define:
phenotype
The outward presentation of an individual based on the genotype.
Phenotypes can be easily observed, such as eye color. Phenotypes are determined by the genotype, or genetic allele combination, of someone’s DNA.
What is a dominant trait?
A trait where only 1 copy of the allele is needed to express the trait.
Dominant traits are expressed in both homozygous dominant (AA) and heterozygous (Aa) individuals, masking the recessive trait.
What is a recessive trait?
A trait expressed only when both alleles are recessive.
A recessive trait will not be observed in the presence of a dominant allele (Aa or AA) but will be expressed in homozygous recessive individuals (aa).
Define:
homozygous genotype
Having two identical alleles for a gene.
A homozygous genotype can be either dominant (AA) or recessive (aa).
Define:
heterozygous genotype
Having two different alleles for a gene.
True or False:
Mutations in genes can lead to changes in traits.
True
Mutations are changes in the DNA sequence that can alter the structure or function of proteins, resulting in new traits.
What are autosomes?
Chromosomes that do not determine sex.
Humans have 22 pairs of autosomes, which carry genes for most traits.
What is a karyotype?
A visual representation of all the chromosomes in a cell.
They are used to study chromosome structure, number, and abnormalities.
Fill in the blank:
The complete set of an organism’s genetic material is called its ________.
genome
The genome includes all the DNA in an organism, including all its genes and chromosomes.
What is the genotype of an individual with a recessive trait?
Homozygous recessive (aa)
A recessive trait can only be observed when both alleles are recessive, meaning the genotype must be aa.
What is the genotype of a homozygous dominant individual?
AA
Homozygous dominant individuals have two copies of the dominant allele, ensuring the dominant trait is expressed.
True or False:
Heterozygous individuals express the recessive trait.
False
Heterozygous individuals (Aa) express the dominant trait, as the dominant allele masks the recessive allele.
What is the result of a homozygous dominant x homozygous recessive cross?
All offspring will be heterozygous.
A cross between homozygous dominant (AA) and homozygous recessive (aa) parents produces offspring with the genotype Aa, all expressing the dominant trait.
True or False:
Two homozygous recessive parents can produce offspring with a dominant trait.
False
Two homozygous recessive parents (aa x aa) can only pass on recessive alleles, so all offspring will express the recessive trait.
What does a Punnett square show?
It shows the probability of offspring genotypes.
Punnett squares help visualize how alleles from both parents combine, providing a probability of different genotype combinations in the offspring.
What is the probability of offspring having a dominant phenotype in a cross between a heterozygous (Aa) and a homozygous recessive (aa) organism?
50%
The Punnett square shows that 50% of the offspring will inherit the dominant allele (A) from the heterozygous parent, resulting in a dominant phenotype (Aa).
What is a sex-linked trait?
A trait controlled by genes located on the X or Y chromosome.
Sex-linked traits are often more common in males because they have only one X chromosome. An example is red-green color blindness, which is X-linked.
Why are sex-linked traits more common in males than in females?
Males have only one X chromosome.
Males inherit their X chromosome from their mother and the Y chromosome from their father. A recessive allele on the X chromosome will be expressed in males because they lack a second X chromosome to mask it.
True or False:
Females must inherit two copies of a recessive allele on the X chromosome for the recessive sex-linked trait to be expressed.
True
Females have two X chromosomes, so they need two copies of the recessive allele (one on each X) to express the recessive sex-linked trait, such as color blindness.
What does a pedigree chart represent?
A family tree that shows the inheritance of traits across generations.
Pedigrees are used to track the inheritance of specific traits, showing the genotypes of family members and how traits are passed through generations.
What is the probability of a child inheriting a recessive trait from two heterozygous (Aa) parents?
25%
The Punnett square shows a 25% chance (aa) of inheriting two recessive alleles, resulting in the expression of the recessive trait.
Fill in the blank:
A ________ cross is a genetic cross involving two traits.
Dihybrid
A dihybrid cross tracks two traits, such as seed color and shape, to observe how they assort independently.
True or False:
In a monohybrid cross, two traits are observed.
False
A monohybrid cross focuses on a single trait, while a dihybrid cross examines the inheritance of two traits simultaneously.
What is the probability of offspring inheriting a dominant trait from a homozygous dominant (AA) and heterozygous (Aa) parent?
100%
All offspring will inherit at least one dominant allele (A), resulting in the expression of the dominant trait.
Define:
Incomplete dominance
A genetic scenario where the heterozygote displays an intermediate phenotype.
In incomplete dominance, neither allele is completely dominant over the other, leading to an intermediate expression of traits. For example, crossing red and white flowers may result in pink flowers.
What is codominance?
Inheritance where both alleles are expressed in the heterozygote.
Codominance occurs when both alleles contribute equally and visibly to the phenotype. An example is the AB blood group, where both A and B alleles are expressed.
True or False:
In incomplete dominance, the heterozygote phenotype is a blend of the two homozygotes.
True
In incomplete dominance, the offspring’s phenotype is a blend of the parental traits, such as pink flowers from red and white flower parents.
What would be the phenotype of a red-flowered (RR) and white-flowered (WW) snapdragon cross in incomplete dominance?
Pink flowers (RW)
Since neither allele is dominant, the resulting phenotype is a blend of the two homozygotes, resulting in pink flowers.
In the case of a black (BB) chicken and a white (WW) chicken, what would be the phenotype of their offspring?
Black and white feathers.
In codominance, both black and white alleles would be expressed equally in the offspring, resulting in speckled feathers.
True or False:
In a cross between two pink (RW) snapdragons, the expected phenotypic ratio is 1 red, 2 pink, and 1 white.
True
The Punnett square for two RW parents shows a 1:2:1 phenotypic ratio: 25% red (RR), 50% pink (RW), and 25% white (WW).
What is a mutation?
A change in the DNA sequence.
Mutations can occur naturally or due to environmental factors like radiation, chemicals, or viruses. These changes can lead to genetic variation, which may or may not affect an organism’s traits.
What are the two main types of mutations?
- Gene mutations
- Chromosomal mutations
Gene mutations affect a single gene, while chromosomal mutations involve changes to the structure or number of chromosomes.
True or False:
Mutations always result in harmful effects.
False
While mutations can be harmful, beneficial, or neutral, not all mutations result in negative outcomes. Some mutations may even provide advantages in certain environments.
What is a point mutation?
A mutation that affects a single nucleotide in DNA.
Point mutations can change one base pair in the gene sequence, potentially altering the protein product. Examples include silent mutations, missense mutations, and nonsense mutations.
Define:
Frameshift mutation
A mutation that shifts the reading frame of the gene.
Frameshift mutations occur when nucleotides are inserted or deleted, causing the sequence to shift and change the downstream codons, which can significantly affect the protein’s function.
What are chromosomal mutations?
Changes in the structure or number of chromosomes.
Chromosomal mutations can include deletions, duplications, inversions, and translocations. They can lead to disorders such as Down syndrome or Turner syndrome.
Fill in the blank:
_________ mutations result in the loss or addition of one or more nucleotides in the DNA sequence.
Frameshift
Frameshift mutations can have severe effects, potentially leading to a completely different protein being made or no protein at all.
What genetic disorder is characterized by an extra copy of Chromosome 21?
Down Syndrome
Down syndrome, or trisomy 21, occurs when there is a third copy of chromosome 21 instead of the usual two, leading to developmental and intellectual disabilities.
What is the most common genetic disorder caused by a mutation in a single gene?
Cystic fibrosis
Cystic fibrosis is caused by mutations in the CFTR gene, leading to the production of thick, sticky mucus that affects the lungs and digestive system.
Fill in the blank:
________ _________ is a chromosomal abnormality characterized by an extra chromosome 13.
Patau syndrome
Patau syndrome (trisomy 13) leads to severe intellectual disability, physical abnormalities, and a shortened life expectancy.
What is the genetic basis of sickle cell anemia?
A point mutation in the hemoglobin gene.
The mutation causes the hemoglobin protein to form abnormally, leading red blood cells to become sickle-shaped, which can block blood flow and cause pain.
What is genetic screening?
A test to detect genetic disorders or risk factors in individuals.
Genetic screening helps identify people who carry genes for genetic disorders, those who might be at risk for conditions like breast cancer, or those who may pass on a genetic condition to their children.
What is the role of genetic counseling?
To support and educate about genetic conditions.
It helps people understand the risk of inherited genetic disorders, make informed decisions, and manage potential health issues. It is useful in cases of inherited diseases, pregnancy, and family planning.
True or False:
Genetic counseling can only be done before pregnancy.
False
Genetic counseling can be beneficial before and during pregnancy, as well as for individuals with existing genetic conditions or concerns about inherited diseases.
What is the purpose of prenatal genetic testing?
To assess the risk of genetic disorders in a fetus.
Prenatal genetic testing, such as amniocentesis or chorionic villus sampling (CVS), helps detect conditions like down syndrome, cystic fibrosis, and sickle cell anemia in unborn children.
