Chapter 12 - Mendelian Genetics & Some Microbio Flashcards
What is complete dominance?
It means that one allele is dominant over the other, so it determines the phenotype whenever it is present. The other allele is recessive.
What is an allele?
A version of the same gene. One gene can have various alleles.
What is a locus?
A physical location of a gene on a chromosme
True or false:
In complete dominance, heterozygotes always display the dominant phenotype.
True
Explain codominance
Codominance is an inheritance pattern in which two alleles contribute equally to an individual’s phenotype.
Example: AB blood type, a flower with red and white stripes
Explain incomplete dominance and give an example.
Incomplete dominance is an inheritance pattern in which the heterozygous phenotype is a blend of the two homozygous traits.
Example: In this pattern, if RR individuals display red coloring and rr individuals are white in color, then Rr flowers would be expected to be pink.
What is incomplete penetrance?
Occurs when various individuals all have identical genotypes and yet some have the disease phenotype and others do not.
What is expressivity?
Expressivity refers to the extent to which an individual’s phenotype is affected by their genotype, and is often a range.
Example: Alleles can be expressed on a various range. A person with the same allele can have severe symptoms of a disorder associated w/ the allele, while another person w/ the same allele has moderate symptoms.
What is genetic leakage?
The transfer of genetic information between two different species.
Example of genetic leakage.
When a hybrid offspring successfully mates with one of its parent species and produces viable offspring. This causes the offspring to contain both hybrid genes and genes from parental species.
Explain Mendel’s 2nd Law of Independent Assortment.
Genes that are located on different chromosomes separate independently during Anaphase.
Explain Mendel’s 1st Law of Segregation.
Alleles separate independently of one another when forming gametes.
Which process of genetic recombination occurs during prophase I of meiosis?
Crossing over, or the trading of DNA segments between homologous chromosomes, occurs when these chromosomes are paired together in prophase I.
What is a mutation, and how does it arise?
A mutation is an alteration in DNA sequence. Mutations arise spontaneously (often from errors in DNA replication) or be induced by mutagenic substances.
Some changes in DNA sequence, known as silent mutations, do not affect the organisms in which they occur. Describe two situations that could lead to a silent mutation.
A silent mutation could be caused by:
A mutation in an intron, or noncoding, sequence
A mutation that replaces one degenerate codon with another
What is evolution?
Evolution is defined as any change in the allelic frequency within a given gene pool across generations.
What are some mechanisms of evolution?
Natural selection
genetic drift
Mutations
Gene flow
What is natural selection? What two things are required in order for it to occur?
- Individual has a different traits that confers an advantage for survival for them.
- Given the advantage of survival, they can reproduce & pass those traits onto future offspring.
What is survival of the fittest?
Survival of the fittest is a term meaning that the individual best suited to its environment will be most likely to survive and pass on its genetic information to future generations.
What are adaptive traits?
Traits that are beneficial to the organism’s evolutionary fitness and aid in survival and reproduction.
What is genetic drift?
Genetic drift describes random changes in allele frequencies in populations that result from random events (natural disasters). More likely to happen in small population.
What are the two types of genetic drift?
Bottleneck effect and founder effect
What is the founder effect?
When a small group of individuals splits off and starts a new population with less genetic variation/diversity than the larger population they came from.
What is the evolutionary bottleneck effect?
A sudden decrease in the number of individuals in a population, limiting the genetic diversity of the species.
What is gene flow?
The introduction of genetic material from one species/population to another population via migration to that population and interbreeding. This causes allele frequencies of two populations to become similar.
What is speciation?
The formation of new species from existing ones.
What is convergent evolution?
When species from different ancestors converge because of development of analogous structures in response to similar environmental conditions.
What is divergent evolution?
Divergence in two species that come from the same ancestor although they have different phenotypic traits. They diverge to produce homologous structures.
If a species diverged from a common ancestor 80 million years ago, what does the graph look like in terms of the # of mutations she has over time?
The # of neutral mutations acquired over time increases.
Name the five prerequisites for Hardy-Weinberg equilibrium.
Hardy-Weinberg equilibrium requires five conditions:
Large population size
No mutation
No inward or outward migration
No natural selection
Random mating
What is pleiotropy?
When one single gene contributes to (more than one) various phenotypes
Which allele in HW equilibrium denotes the dominant allele?
p
Which allele in HW equilibrium denotes the recessive allele?
q
What is the HW equilibrium equation which denotes the fraction of individuals which have a certain genotype?
p^2 + 2pq + q^2 = 1
What is the HW equilibrium equation which denotes the frequency of each allele (p and q)?
p + q = 1
Define what it means for our genetic code to be “degenerate”.
It means that for each amino acid, there can be multiple codons which code for that amino acid. This occurs due to the 3 position in the codon called the wobble position.
True or false:
Mutations aren’t evolutionarily favorable.
False, they do favor evolution and provide genetic variation.
What is the difference between a substitution mutation and a missense mutation?
A substitution mutation simply changes the DNA sequence (substitutes one base to another), but CAN change the amino acid sequence.
A missense mutation requires a change in the amino acid sequence.
What is extranuclear inheritance?
The transfer of DNA that is not located in the nucleus. In eukaryotes, this is associated with mitochondria, which contain their own genes
How many chromosomes does a haploid cell have?
23
What are linked genes? When do they occur?
Genes which are linked together and cross over together.
Linkage occurs, however,
when two genes are very, very close to each other on the same chromosome because at certain
proximity it becomes unlikely that a crossing over event will occur exactly between them.
What is mosaicism? Why is it rare?
Mosaicism is the case in which different somatic cells within the same individual contain non-identical genotypes.
It is rate because all the somatic cells in your body should contain the same set of alleles/genes.
Can females and males both be carriers for an X-linked condition?
No, only females can be carriers. Males have 1 X chromosome which means they will be affected by the disease if they have the bad allele.
What aspect of crossing over violates Mendel’s Law of Independent Assortment?
Linked genes which are more likely to assort into gametes together.
What is a test cross used to determine?
A test cross is used to find the unknown genotype of an individual with a dominant phenotype.
The unknown individual is crossed w/ a homozygous recessive individual and based on the offspring, the parental genotype can be determined.
What are imprinted genes?
Genes that are passed down from parents, which are epigenetically modified (that is methylated) to silence those specific genes on the chromosome. There are about 80 known mammal genes that function in this “imprinted” manner. For a gene coding for insulin growth factor, the maternal copy is expressed while the paternal copy is imprinted, so its inactive.
What did Mendel’s dihybrid cross (two traits) show?
True breeding (homozygous parents) produced all heterozygous offspring.
F2 generation had a 9:3:3:1 phenotypic ratio.
For an imprinted gene, what happens if both the maternal and paternal copy are expressed?
This can lead to serious life-altering conditions, developmental conditions, etc.
What are the different types of prezygotic reproductive isolation (no fertilization occurs)?
Temporal, habitat, behavioral, mechanical, gametic
Temporal isolation
Two species breed at different times
Habitat isolation
Two species live in different habitats
Behavioral isolation
Two species have completely different mating behaviors
Mechanical isolation
Two species have structural differences in reproductive organs
Gametic isolation
The gametes are incompatible with one another, sperm can’t fertilize th egg
What are the forms of postzygotic reproductive isolation (after fertilization)?
hybrid inviability, hybrid sterility, and hybrid breakdown
Hybrid inviability
When the offspring die during development in the womb
Hybrid sterility
When the offspring that is born is sterile and unable to produce future offspring
Hybrid breakdown
When offspring produced in later generations is either sterile or inviable
How do you figure out the genotype frequency when observing two traits?
You draw two monohybrid crosses for the two different genes. Than you multiply 1 frequency from one cross with the other frequency from 2nd cross.
How to answer this type of question:
How many different types of gametes could be produced by an individual with the arbitrary genotype of AAbbCCDdEe?
You take 2^n
n is equal to the # of heterozygote genotypes which is only 2 in this case
so 2^2 = 4 different gametes
AAMC SB Bio #24
AAMC FL4 #58
Use rule for non-mutually exclusive events for calculating probability
- Recognize that genes are unlinked –> meaning events are INDEPENDENT of one another and recognize that the 2 events CAN OCCUR simultaneously, that is the person can have both alleles for deafness –> use special rule
- Rule: probability of (Event A + Event B) - (Event A x Event B)
- Application to problem: (1/2 + 1/4) - 1/8 = 5/8
Rule for mutually exclusive events: Events that CAN’T occur at the same time
Probability of A or B occuring: probability A x probability B
