Lecture 16 - Evolution

Question 1

What are Darwin’s 4 postulates of evolution?

Answer 1

1. Individuals in a species are variable due to mutations
2. Some variations are passed onto offspring
3. More offspring are produced than can survive
4. Survival and reproduction are not random

Question 2

What is the modern synthesis?

Answer 2

Neo Darwinian opinions that consider evolution in terms of change in allele and gene frequencies over time and the average action of selection on genotypes

Question 3

Why does selection differ between haploid and diploid organisms?

Answer 3

In haploid genotype = phenotype = individual but in diploid genetics combinations are disrupted by meiosis therefore the only continuity is allele transmission

Question 4

What will selection aim to do?

Answer 4

Remove less fit variants or increase those with more fitness

Question 5

How do rare mutations invade successfully?

Answer 5

As rare recessive alleles present in heterozygous organisms or as dominant alleles that may remove useful recessive alleles

Question 6

How does genetic drift increase/decrease allele frequencies?

Answer 6

It is the chance different in transmission of alleles that leads to fluctuations in allele frequency

Question 7

What is the primary mechanism for increasing rare recessives?

Answer 7

Genetic drift

Question 8

What can genetic bottlenecks lead to?

Answer 8

The founder effect

Question 9

Why may frequency dependent selection select for rare alleles?

Answer 9

Rare alleles may be less likely to be predated on since they are not recognisable

Question 10

What is the equation for fitness?

Answer 10

Fitness = 1 - selection coefficient (reduction in success of phenotypes)

Question 11

How does selection determine how fast allele frequencies change?

Answer 11

When selection is high allele frequencies change rapidly

Question 12

What is stabilising selection?

Answer 12

Intermediate (mean) variants are selected for, reduces variance eg human birth weight

Question 13

What is directional selection?

Answer 13

Individuals at one extreme are selected for, shifts the mean value eg size of European black bears

Question 14

What is disruptive selection?

Answer 14

Individuals at both extremes are selected for, leads to bimodal distribution eg African fire birds

Question 15

Why is sexual selection needed?

Answer 15

To maximise reproductive success in competition for mates

Question 16

What is kin selection?

Answer 16

Changes in gene frequency across generations driven by interactions between related individuals

Question 17

What is the coefficient of relatedness?

Answer 17

r = (1/2) x n (connection removed from self)

Question 18

What is Hamilton’s Rule?

Answer 18

Cost of not reproducing/ benefit of helping kin to reproduce < relatedness

Question 19

What does rB> C mean?

Answer 19

r = genetic relatedness to the recipient of the altruistic act (defined by the probability that a gene picked randomly from each locus is identical)
B = additional reproductive benefit gained by recipient of altruistic act
C = reproductive cost to individual performing the act

Question 20

What is speciation?

Answer 20

Produces 2 separate species defined as a group of organisms capable of inbreeding to produce female offspring

Question 21

What are the 2 types of speciation?

Answer 21

Allopatric: location
Sympatric: mating time, habit within location

Question 22

How is speciation reinforced?

Answer 22

Pre mating isolation: behavioural choice, spatial constraint, temporal isolation, mechanical incompatibility
Post zygotic isolation: hybrid inviability, hybrid sterility