Population Selection, Structure, & Drift

Question 1

Selection:

Answer 1

Non-random change in the frequency of a genetic variant due to differential fitness

Question 2

Mutation is…

Answer 2

The process by which variants are created for selection to act upon

Question 3

Is the mutation rate large or small

Answer 3

Small, about 2x10^8 per bp

Question 4

If the mutation rate is so small, how are they also so common?

Answer 4

The rate is small (2x10^8 per bp) but the genome is very large (3x10^9bp) so there are lots of opportunities for mutations

Question 5

What is used to describe a variant’s effect on fitness?

Answer 5

Selection coefficient (s)

Question 6

Fitness:

Answer 6

The number of offspring an individual has that survive to maturity

Question 7

To calculate s we normalize the fitness of the background population to…

Answer 7

1

Question 8

The equation for fitness of a homozygous mutant is…

Answer 8

1+2s

Question 9

The equation for fitness of a heterozygous mutant is…

Answer 9

depends on dominance (h)
1+2hxs
h=1 dominant
h=0 recessive
h=0.5 additive variants

Question 10

What is the s value for beneficial, deleterious, and neutral variants respectively

Answer 10

B: s>0
D: s<0
N: s=0

Question 11

What are the types of selection (think bell curves)

Answer 11

Stabilizing
Directional
Diversifying

Question 12

What does the fate of a new mutation depend on?

Answer 12

Selection
Effective population size
Drift

Question 13

What factors need to be large enough in order for selection to overcome drift

Answer 13

s and Ne (effective population size)

Question 14

Mutations are most commonly………..and least commonly………..
In terms of the effect they have

Answer 14

Neutral, beneficial

Question 15

What is the equation for a nearly neutral mutation

Answer 15

|sxNe|<1

Question 16

What percent of all new mutations are lost within one generation due to chance

Answer 16

30%

Question 17

What affectes effective population size

Answer 17

Whether or not mating is random
If the size is stable/fixed
Sex ratio distortion (dairy cattle)

Question 18

What is the loss of AB genotypes called

Answer 18

The Wahlund effect

Question 19

Two populations can fix alternative alleles. This is represented by

Answer 19

Fst
AA: p^2 + Fstpq
AB: 2pq(1-Fst)
BB: q^2 + Fstpq

Question 20

Selections is …………in populations with larger Ne

Answer 20

Stronger

Question 21

Relative efficiency (time until fixation) for codominant v dominant v recessive mutations

Answer 21

Co-dominant - fastest
Dominant - middle, inefficient
Recessive - low, very slow

Question 22

What is a selective sweep

Answer 22

When a positively selected variant drags other variants (regardless of desirability) along with it.because they are located close together. Called genetic hitchhiking or genetic draft.
This reduces diversity and heterozygosity in the region

Question 23

Extreme Fst outliers are a sign of…

Answer 23

Recent adaptation

Question 24

Why do we still have genetic diseases? Isn’t that the point of selection?

Answer 24

Hitchhiking - deleterious mutations linked with positive ones –> not weeded out
Pleiotropy - variants can have multiple phenotypic effects or have different effects in different environments
Drift - small Ne –> strong drift, gives deletrious mutations a chance to increase in frequency