Hard Stuff on Bio 1780 Flashcards Preview

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Flashcards in Hard Stuff on Bio 1780 Deck (22):
1

- What does Heterozygosity depend on? How do they each affect the degree of heterozygosity?

Mutation & population size. Increase in both mutation rate and population size will increase heterozygosity

2

genetic drift

change in allele frequency over time due to random chance

3

how drift affects small populations

higher probability of large jumps in allele frequency any given generation; shorter time to fixation or loss

4

probability of brand new mutation becoming fixed

1/ (2N)

5

relationship between drift and mutation

H = (4Nu)/(1+4Nu)

6

When N gets larger, H ....

increases

7

When u gets larger, H...

increases

8

Define the Bottleneck effect and predict its outcome

Sudden external factor (e.g. natural disaster) that kills most of the individuals in a population, only leaving a
randomly selected small group of individuals. Genetic drift will cause it to evolve from the previous genotypic
frequencies

9

Selection happens when individuals

vary in fitness, due to some having higher rates of survival and/or reproduction

10

Modes of natural selection

1. Purifying selection
2. Directional selection
3. Disruptive selection (favors extreme
phenotypes)
4. Overdominance (heterozygote advantage)
5. Underdominance (heterozygote disadvantage)
6. Frequency dependent selection

11

Common modes of natural selection

purifying and directional (selection acts on phenotypes regardless of genetic basis)

12

Why isn’t purifying selection perfectly effective at removing deleterious alleles

o Not all phenotypic variation has a simple genetic basis
o Deleterious recessive alleles can be sheltered in heterozygotes
 Because paired with other allele that is in some way more beneficial
o Mutation continually introduces genetic variation into population

13

If new mutation is codominant and advantageous

codominant genotype will be selected for at a slow rate, causing a gradual rise in f(B). However, once BB homozygotes are present in the population from the mating of ABxAB, there will be selection for BB even over the codominant case. Thus, allele B will eventually reach fixation, since genotype BB is being selected for above all else; will take more time before initial slope because evolution proceeds more slowly since advantage is small

14

If new mutation is dominant and advantageous

like codominant but initial slope occurs before; may not become fixed or takes longer because A2 alleles will persist because sheltered in heterozygotes but selection will remove it

15

If new mutation is recessive and advantageous

evolution is delayed by selection because everyone has same fitness; allele stays very rare and frequency determined by drift

16

natural selection is strong.....

in large populations

17

if N x s is less than 1 ....

drift is more powerful force, where N is population size and s is strength of selection on selected allele

18

if N x s is greater than 1...

selection is more powerful

19

Heritability (the proportion of trait variance that is genetic) gets small when

environmental contributions to the trait get large

20

Heritability predicts how well population responds to

directional selections

21

R

response to selection; difference between the trait mean in the progeny and the trait mean in parents

22

large S means

strong selection