Genetics of Adaptation

Diversity within a species e.g. sexual dimorphism

Diversity between species

• Mutation • Drift • Migration • selection

A characteristic that enhances the survival or reproduction of organisms that bear it, relative to alternative character states.

p2 + 2pq + q2 = 1

• HWE gives a mathematical baseline of a non-evolving population to which evolving populations can be compared. A null model. • Describes allele frequencies in a population from one generation to the next

• Infinite population (no drift) • No mutations • No selection • Mendelian inheritance • Random mating • No migration

by one of the evolutionary forces 1. mutation 2. genetic drift 3. migration 4. natural selection

Random Only process that brings new variation

Random changes in unselected allele frequency Happens more in smaller populations tends to lower heterozygosity can cause isolation populations to diverge

Counteracts divergence due to drift brings in new variation from previously isolated populations or rare hybridisation events

Fitness and adaptation focussed Differential survival and/or reproduction of [classes of entities] that differ in one or more characteristics

Probability of survival x average number of offspring (combination of survival and reproduction)

The fittest: w = 1 Not so fit: w = 0.5 The most unfit: w = 0 The difference between w and 1 = the selection coefficient (s)

Fitness and selection coefficient are the inverse of one another E.g. if a genotype has a fitness (w) of 0.9 then s would be 0.1 (adds up to 1)

• correlations between trait and environment • Responses to experimental change in the environment • Correlations between trait and fitness component • Signatures in the genome

Is the adaptation just a consequence of physics/chemistry? Genetic drift can spread traits Ancestral state (exaptation - something that’s already present due to other reasons but may also have adaptive features). Selection might not cause any change Selection might not be working at the individual level Linkage - linkage disequilibrium (Alleles appearing together more often than you would expect). Hitchhiking allele

The number of alternative alleles for a gene at a given locus in the population measure of variation ‘The diversity of choices’

• Mutation • sex • Ploidy • balancing selection - Heterozygous advantage - frequency- dependent selection

Somatic Mutation: at the individual level Germline mutation: the only mutations that can be heritable

At the individual level

The only mutations that can be heritable

Substitution insertion deletion inversion

Silent mutations - have no effect on the amino acid