Topic 6

Question 1

what is Natural selection

Answer 1

Differences is survival and reproduction of phenotypes, leading to differences in their contribution to the next generation. This results in a change in the frequency of HERITABLE phenotypic variations (alleles) in population over time.

Question 2

3 requirements for Natural selection

Answer 2

1. phenotypic variation
2. the variation must cause differential survival and reproduction
3. the variations must be heritable

Question 3

Adaptation

Answer 3

• an adaptation is a characteristic or trait that increases an individual’s fitness relative to individuals that do not possess it
• Natural selection is the primary means of adaptive evolution

Question 4

fitness

Answer 4

an individual’s contribution to the next generation, and depends on:

1. survival (viability sel’n)
2. fecundity (# of gametes)
3. ability to obtain a mate

Question 5

Absolute fitness

Answer 5

the average number of offspring (zygotes) contributed to the next generation by an individual (zygote) in this generation
e.g. Waa, Wab, Wbb

Question 6

Relative fitness

Answer 6

Measure of a genotype’s contribution to the next generation RELATIVE to that of other genotypes in the pop’n
(normally scaled to the genotype with the largest absolute fitness)
-eg. Waa=3, Wab=2, Wbb= 0.5
-waa= 1 (3/3), wab= 0.66 (2/3), wbb= 0.17 (0.5/3)

Question 7

Population fitness

Answer 7

• the mean absolute fitness of a population
• denoted: W (with bar on top)
• if the population fitness is greater than 1, the population will increase in size (and vice versa)

Question 8

Relative population fitness

Answer 8

• the average fitness of the entire population relative to those individuals within it that have the highest fitness
• denoted: w (with bar on top)

Question 9

4 components of fitness

Answer 9

1. viability: prob of surviving until reproductive maturity (viability selection)
2. Fecundity: The number of gametes produced (fecundity selection)
3. Mating ability: the ability to obtain a mate (sexual selection)
4. gamete competition: normally sperm competition (some gametes have a higher prob of forming a zygote than others)

Question 10

Antagonistic selection

Answer 10

when any of the following 3 oppose each other:

-viability sel’n, fecundity sel’n, sexual sel’n

Question 11

Single locus model of natural selection assumptions

Answer 11

1. Fitness differences are only due to differences in survival (viability)*****
2. Fitness differences are attributed to a single locus
3. Mating is random
4. No mutation, drift or gene flow occurs
5. Fitnesses are constant and independent of both allele frequencies and pop’n size

Question 12

Equilibrium point

Answer 12

a point where allele frequencies will remain constant
2 major types:
a. stable eq’m
b. unstable eq’m

Question 13

Stable eq’m

Answer 13

• a point of attraction
• allele frequencies approach a point of stable eq’m from a short distance away, and stay in vicinity of the eq’m
• *stable eq’m is GLOBALLY STABLE if it is always approached, regardless of starting conditions

Question 14

Unstable eq’m

Answer 14

a point of repulsion

-allele freq’s move away from the point of unstable eq’m UNLESS there precisely on it

Question 15

adaptive radiation

Answer 15

• the diversification of multiple descendent lineages from a single ancestral lineage
• typically result in ecological specialization and morphological innovation
• driven by nat. sel’n, often by sexual sel’n too

Question 16

punctuated equilibrium

Answer 16

• adaptive radiation typically involve rapid changes (ecological and morphological innovation)
• followed by long periods of stasis

Question 17

sexual selection

Answer 17

differential reproductive success resulting from differential abilities to find a mate

Question 18

Inverse frequency dependent selection

Answer 18

• the LOWER the frequency of a phenotype (genotype), the GREATER its relative fitness
• alleles will always move to a pt of fixation (move away from either A or B)–>ex. of global ..fixation

Question 19

Balancing selection

Answer 19

• any type of selection that acts to maintain genetic variation
  a) heterozygote superiority
  b) inverse frequency dependent selection

Question 20

hitchhiking

Answer 20

when one genotype is dragged to fixation with another genotype because they are linked

-e.g. AABB, aabb–> bb has low fitness hence eliminated by nat. sel’n and aa also eliminated b’x they are linked (even though it has a high fitness)

Question 21

epistasis

Answer 21

• an effect of the interaction of two or more gene loci on phenotypes and/or fitness
• joint effect of the loci is different than the sum of the individual loci taken separately

Question 22

pleiotropy

Answer 22

• a phenotypic effect of a single gene on more than one character
• e.g. drosophila single gene involved in both larval development rate and body size

Question 23

antagonistic pleiotropy

Answer 23

• specific type of pleiotropy
• e.g. nat. sel’n favours rapid larval development rate
  1. this increases survival
  2. but also results in smaller body size & lower fecundity

Question 24

sexually antagonistic genes

Answer 24

sometimes alleles at an autosomal locus can have opposing fitness effects in males and females
-e.g. AA is high fitness in males and low fitness in females

Question 25

adaptive topography

Answer 25

• sewall wright developed a model of “adaptive landscapes”
• there are multiple equilibria and outcomes of selection are far more complex (when traits are controlled by multiple loci)