Lecture 20 Chapter 25 Flashcards
population genetics
○ Study of the distribution and change in frequency of alleles within populations
evolution
change in gene frequency over time in a population
- which leads to speciation and divergence
population
○ A group of interbreeding, sexually reproducing individuals sharing a common set of genes
genetic variation
frequencies affected by evolutionary forces: mutations, gene flow, genetic drift, and natural selection
Hardy-Weinberg Law assumptions and predictions
Allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences - Assumption ○ Population is large, ○ randomly mating, ○ not affected by mutation, ○ No migration ○ No natural selection - Prediction 1 ○ The allelic frequencies of a population do not change - Prediction 2 ○ The genotypic frequencies stabilize
positive assortative mating
a tendency of like individuals to mate
negative assortative mating
a tendency of unlike individuals to mate
Inbreeding
measure of the probability that two alleles are identical by descent
- identical by descent
- -alleles descended from the same copy in a common ancestor e.g hemophillia in royal family
- identical by state
- –alleles that are the same in structure and function but are descended from two different copies in ancestors
inbreeding depression
- increased appearance of lethal and deleterious traits with inbreedng
- inbreeding increases the % of homozygous individuals in the population
outcrossing
the avoidance of mating between related individuals
Natural Selection
○ Differential survival and reproduction of individuals due to differences in phenotype
- frequency of a recessive allele at equilibrium is equal to the square root of the mutation rate divided by the selection coefficient
- the frequency of a dominant allele at equilibrium is equal to the mutation rate divided by the selection coefficient
nonrandom mating
Occurs when the probability that 2 individuals will mate is not the same for all possible pairs of individuals
- occurs when members of 1 biological sex choose mates of the other sex to mate with and compete with members of the same sex for access to members of the opposite sex
mutation
○ A permanent alteration in the DNA sequence that makes up a gene
migration
○ The movement of populations, groups or individuals
In genetic terms, migration enables gene flow: the movement of genes from one population to anoth
genetic drift
The change in the frequency of a gene variant (allele) in a population due to random sampling of organisms
- change in allelic frequency due to chance factors
founder effect
□ The reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors
genetic bottleneck
□ A sharp reduction in the size of a population due to environmental events (such as earthquakes, floods, fires, disease, or droughts) or human activities ( such as genocide)
Fitness
- the relative reproductive success of a genotype compared to other genotypes in the population
- fitness ranges from 0 to 1
- to calc, take the avg # of offspring produced by genotype and divide it by the mean number of offspring produced by the most prolific genotype
selection coefficient
- the relative intensity off selection against a genotype
- equals 1 - the fitness for a particular genotype
directional selection
a type of selection in which one allele or trait is favored over another
overdominance (heterozygote advantage)
heterozygotes are favored over homozygotes and have a reproductive advantage which maintains both alleles in the population
underdominance (heterozygotes selected against)
the heterozygote has a lower fitness than both homozygotes. this leads to an unstable equilibrium
What are some advantages of using allelic frequencies to describe the gene pool of a population instead of using genotypic frequencies?
there are fewer alleles than genotypes, so the gene pool can be described by fewer parameters when allelic frequencies are used. Additionally, the genotypes are temporary assemblages of alleles that break down each generation; the alleles are passed from generation to generation in sexually reproducing organisms
which statement is not an assumption of the Hardy-Weinberg law?
a. the allelic frequencies (p and q) are equal
b. the population is randomly mating
c. the population is large
d. natural selection has no effect
a. the allelic frequencies (p and q) are equal
What is the expected frequency of heterozygotes in a population with allelic frequencies x and y that is in Hardy-Weinberg equilibrium?
a. x +y
b. xy
c. 2xy
d. (x-y)^2
c. 2xy
example: 2 x 0.5 x0.5 = 0.5 or 505
in cats, all-white color is dominant over not all-white. In a population of 100 cats, 19 are all-white. Assuming that the population is in Hardy-Weinberg equilibrium, what is the frequency of the all-white allele in this population?
0.10
p = 1-q = 1 - 0.9 = 0.1
q= square root of f(aa) = square root of 100-19 or the square root of 81 = 9
What is the effect of outcrossing on a population?
a. allelic frequencies change
b. there will be more heterozygotes than predicted by the Hardy-Weinberg law
c. there will be fewer heterozygotes than predicted by the Hardy-Weinberg law
d. genotypic frequencies will equal those predicted by the Hardy-Weinberg law
b. there will be more heterozygotes than predicted by the Hardy-Weinberg law
When a population is in equilibrium for forward and reverse mutation rates, which of the following is true?
a. the number of forward mutations is greater than the number of reverse mutations
b. no forward or reverse mutation occur
c. the number of forward mutations is equal to the number of reverse mutations
d. the population is in Hardy-Weinberg equilibrium
c. the number of forward mutations is equal to the number of reverse mutations
Each generation, 10 random individuals migrate from population A to population B. What will happen to allelic frequency q as a result of migration when q is equal in populations A and B?
a. q in A will decrease
b. q in B will increase
c. q will not change in either A or B
d. q in B will become q^2
c. q will not change in either A or B
Which of the following statements is an example of genetic drift?
a. Allele g for fat production increases in a small population because birds with more body fat have higher survivorship in a harsh winter
b. random mutation increases the frequency of allele A in one population but not in another
c. Allele R reaches a frequency of 1.0 because individuals with genotype rr are sterile
d. Allele m is lost when a virus kills all but a few individuals and just by chance none of the survivors possess allele m
d. Allele m is lost when a virus kills all but a few individuals and just by chance none of the survivors possess allele m
The average numbers of offspring produced by three genotypes are: GG = 6, Gg = 3, gg = 2. What is the fitness of Gg?
a. 3
b. 0.5
c. 0.3
d. 0.270
b. 0.5
fitness ranges from 0 to 1
to calculate, take then mean # of offspring produced by a genotype and divide it by the mean # of offspring produced by the most prolific genotype
so 3/6 = 0.5
How does overdominance differ from directional selection?
In overdominance, the heterozygote has the highest fitness and both alleles are maintained. In directional selection, selection causes one allele or trait to increase in frequency.
Genome-wide association studies:
a. attempt to correlate disease with DNA variations
b. assess very large numbers of SNPs (more than 10,000)
c. explain most of the genetic variability in disease such as cardiovascular disease
d. identify multiple loci involved in complex traits
e. A and B and C
E. A and B and C
