Natural Selection

Question 1

What is evolution?

Answer 1

Descent with modification that leads to changes in allele frequency

Question 2

What are the three requirements for evolution by natural selection to happen?

Answer 2

1. Variation in phenotypic traits
2. Inheritance of traits from a genetic basis that is heritable
3. Differences in (offspring) production between certain traits

Question 3

What are the 3 levels of fitness?

Answer 3

1. At the individual level
2. At the genotypic level
3. At the allele level

Question 4

At the individual level, what does fitness refer to?

Answer 4

The contribution of an individual with a specific phenotype to the next generation

Question 5

What are the three components of individual fitness?

Answer 5

1. Survival to mating age
2. Mating success - number of partners
3. Fecundity - ability to provide an abundance of offspring

Question 6

What is fitness at the level of the genotype?

Answer 6

It is the contribution a genotype makes to the gene pool of the next generation relative to other genotypes

Question 7

What is the formula to determine relative fitness given the survival and reprotductive rates of genotypes

Answer 7

(Survival Rate*reproduction rate) / largest number of the group to get ratio

Question 8

What does the term lower case s indicate in evolution?

Answer 8

Selection coefficient - The relative strength of selection for or against a genotype

Question 9

How do we denote the relative fitnesses of a heterozygote population with 3 genotypes? What do the variables mean?

Answer 9

A1A1 = 1
A1A2 = 1-hs
A2A2 =1-s

S - selection coefficient
h - dominance coefficient (dominance of A1 would mean h=0)

Question 10

Is dominance based on a specific allele or is it an interaction between alleles?

Answer 10

It is an interaction between two alleles

Question 11

Why is it complicated to determine the effect of a single allele on contribution to the next generation?

Answer 11

1. Alleles do not act alone
2. Alleles express as genotypes, which express as phenotypes meaning there are two layers in between alleles and fitness generation

Question 12

What is the average excess fitness of an allele?

Answer 12

The difference between the average fitness of individuals with the allele and average fitness of all individuals

Question 13

How is the average excess fitness of an allele denoted?

Answer 13

alpha - A1

Question 14

What is the formula for average excess fitness?

Answer 14

Alpha - A1 = p(A1A1 fitness - average fitness) + q(A1A2 fitness - average fitness)

Question 15

How do we denote allele frequencies after mating/selection?

Answer 15

P, H, and Q*

Question 16

What are the formulae for allele frequencies after mating/selection?

Answer 16

P* = p^2*fitness of A1A1

can be standardized by average fitness

Question 17

What is the formula for total average fitness?

Answer 17

P+H+Q*
Sum of all allele frequencies after fitness selection

Question 18

What is the final formula for the change in allele frequencies between generations with natural selection acting?

Answer 18

Change in p = p*(average excess fitness of A1/ total average fitness)

Question 19

What are the key takeaways from the change in allele frequency formula?

Answer 19

1. It can be negative, which determines wether frequency will increase or decrease
2. Selection depends on the frequency of the allele as well, there will be less effect on smaller starting populations

Question 20

What is the equilibrium described when talking about fitness? What is it called?

Answer 20

The mutation - selection balance is the equilibrium between mutation for a deleterious allele and selection against it

Question 21

What are the two types of equilibria?

Answer 21

Stable (states near the equilibrium will converge towards it) and unstable (states near the equilibrium will move away)

Question 22

Define equilibrium

Answer 22

A steady state that will not changed if started at certain conditions

Question 23

What are the two large categories of selection?

Answer 23

Frequency independent - fitness is not dependent on frequency in the population

Frequency dependent - fitness changes depending on phenotype frequency

Question 24

What are the types of frequency independent selections?

Answer 24

Directional Selection, over dominance, and under dominance

Question 25

What is direction selection?

Answer 25

When one allele is favoured over the other

Question 26

How is directional selection noted mathematically?

Answer 26

It favours A1 if w11>w22 It favours A2 if W22>w11

Question 27

What is the allele consequence of directional selection over time?

Answer 27

Fixation of an allele, which is a stable equilibrium

Question 28

What fitness variable affects the rate of fixation?

Answer 28

The strength of the selection coefficient

Question 29

What is over dominance?

Answer 29

It is heterozygote advantage, where selection favours the heterozygote genotypes

Question 30

What is the allele consequence of over dominance selection over time?

Answer 30

A heterozygote stable equilibrium will be reached where both alleles are at intermediate frequencies

Question 31

What is under dominance?

Answer 31

It is a heterozygote disadvantage, where W11>W12

Question 32

What is the allele consequence of under dominance selection over time?

Answer 32

One allele will be lost, as starting with heterozygotes would make an unstable equilibrium that moves in a random direction

Question 33

What is positive frequency dependent selection?

Answer 33

It is selection for the most common phenotype

Question 34

What is the allele consequence of positive frequency dependent selection over time?

Answer 34

One of the alleles will become fixed

Question 35

What is the allele consequence of negative frequency dependent selection over time?

Answer 35

Both alleles will tend to persist

Question 36

What is negative frequency dependent selection?

Answer 36

Phenotypes are favoured when they are rare