Lecture 16 - Evolution Flashcards
What are Darwin’s 4 postulates of evolution?
- Individuals in a species are variable due to mutations
- Some variations are passed onto offspring
- More offspring are produced than can survive
- Survival and reproduction are not random
What is the modern synthesis?
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
Why does selection differ between haploid and diploid organisms?
In haploid genotype = phenotype = individual but in diploid genetics combinations are disrupted by meiosis therefore the only continuity is allele transmission
What will selection aim to do?
Remove less fit variants or increase those with more fitness
How do rare mutations invade successfully?
As rare recessive alleles present in heterozygous organisms or as dominant alleles that may remove useful recessive alleles
How does genetic drift increase/decrease allele frequencies?
It is the chance different in transmission of alleles that leads to fluctuations in allele frequency
What is the primary mechanism for increasing rare recessives?
Genetic drift
What can genetic bottlenecks lead to?
The founder effect
Why may frequency dependent selection select for rare alleles?
Rare alleles may be less likely to be predated on since they are not recognisable
What is the equation for fitness?
Fitness = 1 - selection coefficient (reduction in success of phenotypes)
How does selection determine how fast allele frequencies change?
When selection is high allele frequencies change rapidly
What is stabilising selection?
Intermediate (mean) variants are selected for, reduces variance eg human birth weight
What is directional selection?
Individuals at one extreme are selected for, shifts the mean value eg size of European black bears
What is disruptive selection?
Individuals at both extremes are selected for, leads to bimodal distribution eg African fire birds
Why is sexual selection needed?
To maximise reproductive success in competition for mates
What is kin selection?
Changes in gene frequency across generations driven by interactions between related individuals
What is the coefficient of relatedness?
r = (1/2) x n (connection removed from self)
What is Hamilton’s Rule?
Cost of not reproducing/ benefit of helping kin to reproduce < relatedness
What does rB> C mean?
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
What is speciation?
Produces 2 separate species defined as a group of organisms capable of inbreeding to produce female offspring
What are the 2 types of speciation?
Allopatric: location
Sympatric: mating time, habit within location
How is speciation reinforced?
Pre mating isolation: behavioural choice, spatial constraint, temporal isolation, mechanical incompatibility
Post zygotic isolation: hybrid inviability, hybrid sterility
