Lecture 9a

Question 1

What is evolution?

Answer 1

Change in genetic structure of a population from one generation to the next

Question 2

What is a population (deme)?

Answer 2

A localized group of inter-breeding individuals

Question 3

What is a gene pool?

Answer 3

All alleles at all loci for all breeding members of the population. The sum total of alleles in a population.

Question 4

What are the two components of genetic structure?

Answer 4

genotype frequencies + allele frequencies for a specific population

Question 5

What is genotype frequency?

Answer 5

The fraction of individuals with a certain genotype

of individuals with certain genotype) / (total # individuals in population

Question 6

What is allele frequency?

Answer 6

The fraction of one particular allele at a given locus

of copies of allele in gene pool) / (total # alleles at that locus

Question 7

What is Hardy-Weinberg Law?

Answer 7

p^2 + 2pq + q^2 = 1.0

Question 8

What are assumptions made under Hardy-Weinberg Equilibrium?

Answer 8

• Mating is random
• Large population
• No migration (in or out)
• No mutation
• No selection (equal viability)
• Neither gene nor genotype frequencies change from one generation to the next

Question 9

What assumptions are made when calculating allele frequency?

Answer 9

• All individuals produce an equal number of gametes

- Individuals produce gametes in proportion to their genotype

Question 10

What dos f’ mean?

Answer 10

frequency of the next generation

Question 11

Do allele frequencies change from one generation to the next under HW conditions?

Answer 11

No

Question 12

If HW assumptions are met, is there change in the genetic structure of the population?

Answer 12

No. There is no evolution. It does not matter whether alleles are dominant or recessive.

Question 13

Practice: In some African populations, 1 in 1100 individuals shows a form of albinism. What is the allele frequency for this trait and what proportion of the population are carriers for it?

Answer 13

q = SqrRoot(1/1100) = 0.03
p = 1 - 0.03 = 0.07
2pq = 2(0.03)(0.07) = 0.0582 = f(carrier)

Question 14

Practice: Androgenic alopecia is an X linked trait frequent in European populations. If 71% of males are afflicted, what proportion of females are free of this allele?

Answer 14

f(a) = 0.71 = q
f(A) = 0.29 = p
f(females AA) = p^2 = 0.0841

Question 15

Practice: Two formerly isolated subpopulations are brought together. If the new population consists of 60% RR individuals and 40% rr individuals, what will be the distribution of genotypes in the next generation, assuming HW conditions?

Answer 15

p = 0.6 = f(RR)
q = 0.4 = f(rr)
f'(RR) = p^2 = 0.36
f'(Rr) = 2pq = 0.48
f'(rr) = q^2 = 0.16

Question 16

What does small population size lead to?

Answer 16

Genetic drift, bottleneck effect, founder effect, effective populations size

Question 17

What is genetic drift?

Answer 17

Change in allele frequencies due to sampling error, can lead to loss or fixation of an allele. Drift is a random process.

Question 18

T/F: The frequency of an allele is equal to its probability of fixation.

Answer 18

True

Question 19

What assumption is made when considering genetic drift?

Answer 19

Assume that A and a alleles do not confer differences in viability or reproductive success to the individual that carry them. A/A, A/a, and a/a are equally likely to survive and reproduce.

Question 20

What is founder effect?

Answer 20

A new population of much smaller size can suddenly form when a relatively small number of the members of a population migrate to a new location and establish a new population. The migrants, or “founders,” of the new population may not carry all the alleles present in the original population, or they may carry the same alleles but at different frequencies. Genetic drift caused by random sampling of the original population to create the new population.

Question 21

What is bottleneck effect?

Answer 21

Human intervention shrinks population. Survivors may not be representative of parent population. Can cause an increase in inbreeding. The reduction of population size during a bottleneck increases the level of drift in a population.

Question 22

What is effective population size?

Answer 22

The number of breeding individuals may be much lower than population size. For example, one male bird may scare off other male birds from females and he will therefore pass on his genes more than the other male birds.

Question 23

What is migration (gene flow)?

Answer 23

The movement of individuals (or gametes) between populations. Mating between subpopulations of the same species. This can bring new alleles into a populations. Tends to reduce variation between subpopulations.

Question 24

How do mutations effect allele frequencies?

Answer 24

Creates new alleles, changes allele frequency slightly, depends on mutation rate in organism (# mutations/genome/generation). SNP mutation rate is lower than microsatellite mutation rate.

Question 25

About how many mutations does each child have from their parents?

Answer 25

5-150 More from father than mother because sperm are continuously made and have more divisions. However , most mutations have no functional consequence.

Question 26

What are the effects of non-random mating?

Answer 26

Changes in proportion of homozygotes compared heterozygotes. - Non random mating by itself changes genotype frequency only - Non random mating with selection may reduce on homozygote changing allele frequency

Question 27

What is positive vs negative assortative mating?

Answer 27

Assortative mating is mating based on phenotype. Positive: Similar phenotype more likely to mate which increases homozygosity of that trait. Negative: Opposite phenotypes more likely to mate which increases heterozygosity of that trait.

Question 28

What are the effects of isolation by distance?

Answer 28

Near neighbors more likely to mate than distant strangers. Allele frequency varies between subpopulations especially if they are small or isolated. There is an increase in homozygosity across all traits.

Question 29

What are the effects of inbreeding?

Answer 29

There is an increase in homozygosity across all traits. Inbreeding depresses heterozygotes and increases homozygotes. Inbreeding can intensity distinctive character or concentrate some talent.

Question 30

What is the inbreeding coefficient F?

Answer 30

The probability that two alleles in an individual trace back to the same copy in a common ancestor

Question 31

What is the general formula for the inbreeding coefficient F?

Answer 31

``` F = (0.5)^n(1+FA) n = # of individuals in inbreeding loop other than I FA = inbreeding coefficient of ancestor ```

Question 32

What is FA if the ancestors are not inbred?

Answer 32

FA = 0

Question 33

What is the formula for the inbreeding coefficient when multiple ancestors are shared (multiple loops)?

Answer 33

F = sum[(0.5)^n(1+FA)] Example: [(0.5)^3(1-FA1)] +[(0.5)^3(1-FA2)] Box 18-2 pg 681

Question 34

How you find the f(AA), f(Aa), and f(aa) for inbreeding?

Answer 34

f(AA) = p^2 + pqF f(Aa) = 2pq -2pqF f(aa) = q^2 + pqF Inbreeding reduces frequency of heterozygotes by 2pqF and adds half this amount of homozygote classes

Question 35

If the inbreeding coefficient F=1 what is the f(AA)? f(aa)?

Answer 35

``` f(AA) = p f(aa) = q ```

Question 36

What is selection?

Answer 36

Differential reproductive success. Selection can be artificial or natural. It is the most pervasive and powerful of all causes of evolution. It can change allele frequency quickly even in a large population.

Question 37

What is absolute fitness?

Answer 37

The number of offspring an individual has

Question 38

What is relative fitness?

Answer 38

The fitness of an individual relative to some other individual, usually the most fit.

Question 39

What is biological fitness?

Answer 39

The relative reproductive contribution to the next generation

Question 40

How can selection change allele frequency?

Answer 40

It change allele frequency quickly even in large populations. Selection is adaptive making organisms better suited to their environment. - Favored dominant quickly increases but plateaus. The disfavored recessive is hidden in heterozygote. - Favored recessive takes longer to spread but ultimately fixes first. Advantage is only when homozygous.

Question 41

What are the three types of selection?

Answer 41

Directional: moves the frequency of an allele in one direction until it reaches fixation or loss. Shift towards new phenotype when exposed to environmental changes Disruptive: increases genetic variance when natural selection selects for two or more extreme phenotypes that each have specific advantages. Stabilizing: results in a decrease of a population's genetic variance when natural selection favors an average phenotype and selects against extreme variations.

Question 42

How has DNA shown evidence of past selection?

Answer 42

- There is less diversity in sequence after "selective sweep" (when a favorable allele reaches fixation) - There is more diversity when there is balancing selection

Question 43

What is balancing selection?

Answer 43

If the heterozygous class has a higher fitness than either of the homozygous classes, then natural selection will favor the maintenance of both alleles in the population. natural selection will move the population to an equilibrium point at which both alleles are maintained in the population.

Question 44

What is the direction of natural selection?

Answer 44

Natural selection results form the adaptation to the PARENT'S environment. Direction may reverse if environment fluctuates.