Biol 415: Lecture 10 (10/1/15)

Front 1

Define: Genetic Drift

Back 1

The process of change in allele frequency due solely to chance effects of the random sampling of gametes during reproduction

Front 2

Define: Founder Effect

Back 2

A type of genetic drift where a small population moves from one area to another area. In doing so, this greatly affects the allelic diversity in the new population.

Front 3

Which of the following is true in regards of allelic diversity?

A. Ocean has greater allelic diversity than Australia

B. Hawaii has greater allelic diversity than Oceana

C. Australia has less allelic diversity than Hawaii

D. Hawaii has less allelic diversity than Australia

Back 3

D. Hawaii has less allelic divesity than Australia.

Front 4

The Larger the population size, the ___________ the process of fixation will take

Back 4

Longer

Front 5

If mutations are not introduced in a population that undergoes genetic drift, what will happen?

Back 5

The population will eventually lead to fixation and loss.

Front 6

Uncertainty in allele frequency in the next generation gets smaller as population size gets ____________

Back 6

Bigger

Front 7

Smaller uncertainy in the next generation means that the process of drift till fixation will _____________

Back 7

Take longer

Front 8

Because the population size is ___________, there is small uncertainty in the allele frequency in the next generation and thus fixation will take longer

Back 8

Large

Front 9

Because the population size is ______________, there is large uncertainty in the allele frequency in the next generation and thus fixation will occur shortly

Back 9

Small

Front 10

Which of the following is NOT true

A. Every population follows a unique and random evolutionary ath

B. Genetic drift has fater, greater effect in smaller population.

C. Genetic drift cause changes in llele frequency over time.

D. None of the above

Back 10

None of the above

Front 11

Define: Population Size (N)

Back 11

The total number of individuals in a population, however the relavent size consists of only those individuals that actively participate in the reproductive process.

Front 12

Define: Effective population size (Ne)

Back 12

The size of an ideal population that has the same properties with respect to allele frequency variance, and magnitude and genetic drift as our actual population. This population follows the Wright-Fisher model (genetic drift model) and shows a binomial distribution.

Front 13

T/F: The population size is usually much smaller than the effective population size

Back 13

False. the effective population size is much smaller than the population size.

Front 14

What factors contribute to the fact that the effective population size (Ne) is much smaller than population size (N)

Back 14

1. Overlapping gnerations

2. Variation in the number of offspring among individuals

3. Number of males involved in reproduction is different from the number of females

4. ong-term variations in opulation size

5. Bottlenecks

Front 15

What happens to heterozygosity when a population is drive by genetic drift?

Back 15

Heterozygosity decreases

Front 16

Which of the following is NOT true in regards to heterozygosity

A. Heterozygosity is the frequency of heterozygotes in the population

B. Heterozygosity increases as genetic drift drives a population

C. Heterozygosity is the probability that two alleles chosen at random from the population are different from each other

D. Heterozygosity can be used to measure the genetic diversity in the population

Back 16

B. Heterozygosity increases as genetic drift drives a population

Front 17

Heterozygosity decreases at a rate of

Back 17

1/2N

Front 18

Whose experiment helped to support the theory that heterozygosity is lost in populations which are going through genetic drift. Describe the experiment

Back 18

Buri (1956) took 107 populations of fruitflies each with 8 males and females. All founders were heterozygotes (Bw75/Bw) and every generation another 16 (8 males and females) were picked at random to breed. He found that by generation 19 the Bw75 allele was lost in 30 populations and fixed in 28 populations. He found that the frequency of heterozygotes declined with time.

Front 19

What was the effective population size in Buri's experiment

Back 19

9

Front 20

If small populations are more prone to random fixation events, do smaller populations have overall lower genetic variation

Back 20

Yes, small populations have lower polymorphism and allelic richness thus they have less genetic diversity.

Front 21

If drift decreases variation within population, and alleles eventually either go to fixation or get lost how can variation exist in a population?

Back 21

Mutations. As drift removes variation from the population, mutation introduces new variation into the population, these two opposing forces reach balance (mutation-drift equilibrium) that maintains variation in the population

Front 22

Define: substitution

Back 22

The fixation or replacement of the old allele by the new allele

Front 23

What is the formula used to determine the fixation probability (P) for a population undergoing genetic drift for a netural mutation (i.e., S=0)

Back 23

P=1/2N

N=population

The fixation probability of a new mutation that is governed by drift is equal to its original frequency in the population. Mot new mutations, if not udner selection, will disappear shortly after they arise.

Front 24

What is the formula used to determine the fixation probability (P) for a population undergoing genetic drift who has a positive values of s and large values of N?

Back 24

P~2s

S= selection coefficient

The fixation probability of a new mutation under selection is determined by the selection coefficient. If the increase in fitness is large, the probability of fixation increases.

Front 25

How would you know if a population is being driven by selection or drift?

Back 25

You know if it is selection if alleles move in the same direction in different population sizes. Drift is primarily based on population size and that small population size results in drift being the dominant force.

Front 26

If 2Nes is zero what are the chances of an allele becoming fixed?

Back 26

1/2n

Front 27

If 2Nes is greater than zero what are the chances of an allele becoming fixed?

Back 27

The probability of fixation increase due to larger population size o strong selection

Front 28

If 2Nes is less than 0 what are the chances of an allele becoming fixed?

Back 28

Almost no chance. it is a deleterious mutation

Front 29

How is the rate of substitution of neutral alleles obtained?

Back 29

By multiplying the total number of mutations by the probability of their fixation.

Front 30

Define: Rate of Gene (or allele) substitution

Back 30

Number of substitutions per generation

Front 31

What is the formula to determining the rate of gene (or allele) substitution

Back 31

The rate of substitution is equal to th rate of mutations.

K=u

Front 32

In a large population, the number of mutations arising in every generation is _______, but the fixation probability of each mutation is ________

Back 32

High, Low

Front 33

In a small population, the number of mutations arising in every generation is _______, but the fixation probability of each mutation is ________

Back 33

Low, High

Front 34

T/F: Functionally important parts of the amino acid sequence evolve more slowly than other parts

Back 34

True

Front 35

T/F: nonsynonymous substitutions accumulate faster than synonymous substitutions

Back 35

False. Synonymous substitutions accumulate faster than nonsynonymous substitutions

Front 36

T/F: Rates of nucleotide substitutions vary among genes and among sites within genes

Back 36

True

Front 37

Define: Neutral Theory

Back 37

Molecularly fixed by drift.

Front 38

What type of distribution does an allele undergoing genetic drift display until it reaches fixation/loss?

Back 38

Binomial distribution

Front 39

Which of the following is NOT true:

A. Smaller uncertainty in the next generation means the process of drift till fixation will take longer

B. Uncertainty in allele frequency in the next generation gets smaller as population (N) gets smaller

C. Uncertainty in allele frequency in the next generation gets larger as population (N) gets smaller

D. Larger uncertainty in the next generation means the process of drift till fixation is shorter.

Back 39

B. Uncertainty in allele frequency in the next generation gets smaler as population size (N) gets larger.

Front 40

Explain why smaller populations would lead to larger uncertainty.

Back 40

Smaller populations are vulnerable to random fluctuations in allelic frequency. This random fluctuation translates to large uncertainty as to whether the allele will become fixed or lost.

Front 41

Which population size will result in the slowest loss of heterozygosity?

A. 20

B. 80

C. 100

D. 160

Back 41

A. 20