Lecture 20 Chapter 25

Question 1

population genetics

Answer 1

○ Study of the distribution and change in frequency of alleles within populations

Question 2

evolution

Answer 2

change in gene frequency over time in a population

- which leads to speciation and divergence

Question 3

population

Answer 3

○ A group of interbreeding, sexually reproducing individuals sharing a common set of genes

Question 4

genetic variation

Answer 4

frequencies affected by evolutionary forces: mutations, gene flow, genetic drift, and natural selection

Question 5

Hardy-Weinberg Law assumptions and predictions

Answer 5

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

Question 6

positive assortative mating

Answer 6

a tendency of like individuals to mate

Question 7

negative assortative mating

Answer 7

a tendency of unlike individuals to mate

Question 8

Inbreeding

Answer 8

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

Question 9

inbreeding depression

Answer 9

• increased appearance of lethal and deleterious traits with inbreedng
• inbreeding increases the % of homozygous individuals in the population

Question 10

outcrossing

Answer 10

the avoidance of mating between related individuals

Question 11

Natural Selection

Answer 11

○ 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

Question 12

nonrandom mating

Answer 12

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

Question 13

mutation

Answer 13

○ A permanent alteration in the DNA sequence that makes up a gene

Question 14

migration

Answer 14

○ The movement of populations, groups or individuals

In genetic terms, migration enables gene flow: the movement of genes from one population to anoth

Question 15

genetic drift

Answer 15

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

Question 16

founder effect

Answer 16

□ The reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors

Question 17

genetic bottleneck

Answer 17

□ 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)

Question 18

Fitness

Answer 18

• 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

Question 19

selection coefficient

Answer 19

• the relative intensity off selection against a genotype

- equals 1 - the fitness for a particular genotype

Question 20

directional selection

Answer 20

a type of selection in which one allele or trait is favored over another

Question 21

overdominance (heterozygote advantage)

Answer 21

heterozygotes are favored over homozygotes and have a reproductive advantage which maintains both alleles in the population

Question 22

underdominance (heterozygotes selected against)

Answer 22

the heterozygote has a lower fitness than both homozygotes. this leads to an unstable equilibrium

Question 23

What are some advantages of using allelic frequencies to describe the gene pool of a population instead of using genotypic frequencies?

Answer 23

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

Question 24

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

Answer 24

a. the allelic frequencies (p and q) are equal

Question 25

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

Answer 25

c. 2xy | example: 2 x 0.5 x0.5 = 0.5 or 505

Question 26

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?

Answer 26

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

Question 27

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

Answer 27

b. there will be more heterozygotes than predicted by the Hardy-Weinberg law

Question 28

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

Answer 28

c. the number of forward mutations is equal to the number of reverse mutations

Question 29

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

Answer 29

c. q will not change in either A or B

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

How does overdominance differ from directional selection?

Answer 32

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.

Question 33

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

Answer 33

E. A and B and C