pop gen 6 - multi loci Flashcards
frequency of chromosome type XAB etc relationship with allele frequencies if INDEPENDANT ASSORTMENT
XAB = PA*PB (freq of A allele * freq of B allele)
chromosome frequency = product of component allele frequencies
Disequilibrium definition
Represented by D
OR linkage disequilibrium or gametic-phase disequilibrium
measures genetic associations among two loci
Recombination
Disequilibrium formula
D = XAB * Xab - XAb * XaB
Positive disequilibrium
more likely AB and ab
negative disequilibrium
more likely Ab and aB
recombination
occurs during meiosis in sexual organisms to generate gametes carrying new combinations of alleles
Recombination rate
rec. rate (r) between two loci determines the probability of a cross-over between them creating non parental gametes
chance of having each possible combination of alleles in gametes
Parental -> (1 - 2)/2
Recombinant -> r/2
In what case does recombination actually CHANGE genotype of gametes produced (into recombinant)
If parents differ at BOTH genes
difference between disequilibrium and recombination
disequilibrium is measure of ASSOCIATION
recombination is measure of GENETIC DISTANCE (physical)
genetic hitchhiking
linkage disequilibrium between a selected and a neutral locus can cause alleles at the neutral locus to change in frequency
Selection causing disequilibrium
If certain combinations of alleles work well together, organisms with those combos have greater fitness thus those allele combinations increase in frequency
epistasis
expression of one gene is modified by expression of one or more independently inherited gene, can result in disequilibrium by natural selection
how can mean fitness decline over time?
recombination can form less fit allele combinations despite natural selection favouring other ones
recomb breaking apart combinations that work well together
implications of mean fitness possibly decreasing if both sites are under selection
Evolutionary change in a genome will not always increase adaptation
Evolution doesn’t “optimize” populations, but instead works through the combined processes of selection, mutation, recombination, and drift
causes of evolution other than natural selection
Mutations
Change
Sex and recombination
Alleles favoured for effects on some traits may affect other traits (pleiotropy)
Neighbouring alleles in the genome can be dragged with selected alleles (hitchhiking)
Pleiotropy
Alleles favoured for effects on some traits may affect other traits
