Variation - 5 Flashcards
What are the 3 general models for evolution
- classical model
- balance/selectionist model
- neutral model
Define classical model of evolution
mutations can be good or bad, but it doesn’t matter because there are not many of them
believed there were low levels of polymorphism
Define balance/selectionist model
believed there is lots of polymorphism and that most individuals were heterozygous or had some sort of variation or mutation.
believed speciation wasn’t rare because of the abundance of variation. The variation allowed for natural selection to occur
Define neutral model in evolution
believed that most mutations are deleterious, but natural selection rapidly removes them which results in most of the mutations being neutral. Suggests that mutations don’t make a significant impact on variation
variation is due to random chance.
What model is most strongly accepted
balance/selectionist model
What are the 2 types of summary statistics to determine how much variation occurs
- haplotype diversity
- allelic diversity (% polymorphic sites or heterozygosity)
Define haplotype diversity
measure of how many haplotypes there are in a population and how common they are
Define % polymorphic sites
multiple alleles at a single locus
What are the two ways heterozygosity can be measured to determine variation
- the frequency of heterozygotes
- the fraction of genes that are heterozygous
What determines phenotype
- genotype
- environment (phenotypic plasticity, usually cause range ex. flowers could be red to pink)
- maternal effects (ex. red flower if parents two years old, pink if mother is four years old)
- genomic imprinting (depends on if gets gene from mother or father on how its expressed)
Can phenotype be used to determine genotype
No, because phenotype may not be on a single gene or the phenotype may not be heritable
Instead of using phenotype to determine genotype, what can be used
DNA, because it is a powerful tool to get down to the base layer
What creates variation (4)
mutation, recombination, gene flow, and hybridization
What does the dn/ds ratio tell us evolution at a locus is due to
dn = nonsynonymous (phenotype change), ds = synonymous (no phenotype change)
dn/ds = 1 (drift)
dn/ds<1 -negative/purifying (nonsynonymous are deleterious, so selection gets rid of mutation)
dn/ds>1 - positive/diversifying (means more AA changes than neutral, generally means mutation has benefit)