EE Lecture 4: Natural Selection Flashcards
define adaptation
a characteristic that enhances survival or reproduction relative to alternative characters - often derived relative to the ancestral state and is the result of natural selection
what is a characteristic that enhances survival or reproduction relative to alternative characters called
an adaptation
what is fitness measured in
reproductive success
what is fitness a property of
genotypes, phenotypes or popns NOT individuals
what is fitness NOT a property of
fitness is not a property of individuals
define fitness
the average number of offspring that survive to reproductive age
what is the word eqtn for fitness
fitness = average fecundity x average survivorship
what does fitness describe
the growth rate of the popm
what is fecundity
actual reproductive rate of an org/popn
what is fecundity measured by
the number of gametes produced by an org
what two things are determined for fitness measurements
- fecundity
2. average survivorship
what does selection act on
phenotypes
what is selection caused by
environment
what does selection involve
non random survival and reproduction of phenotypes
what is the greatest fitness an org can reach? (in number)
1
give relative fitness of all possible alleles
WAA, Waa, WAa
how do you work out expected genotype frequencies for after selection
do genotype frequencies before selection then multiply by the relative fitness
eg. AA = p^2(WAA)
what symbol is used to determine the relative fitness
W
what does W mean
relative fitness
what does wbar (W with bar on top) mean
popn average fitness
draw eqtn linking relationship between allele and genotype frequencies after selection
p^2(WAA) + 2pq(WAa) + q^2(Waa) = w bar
how do you work out pā (new allele freq) after selection
pā = [p^2(WAA) + pq(WAa)]/w bar
which phenotype does selection favour
dominant phenotype
which phenotype does stabilizing selection favour
intermediate
discuss selection for vivax malaria resistance
Plasmodium vivax requires DARC protein on RBC to enter and infect cells - duffy null mutation results in loss of DARC expression - duffy null phenotype resistant to vivax malaria
what protein does Plasmodium vivax require on RBC to enter and infect cell
DARC protein
what does a duffy-null mutation result in the loss of
duffy null mutation results in the loss of DARC expression
what is the result of the Duffy-null phenotype
vivax malaria resistance conferred from duffy-null phenotype
what does MHC stand for
major histocompatability complex
what is the MHC
set of cell surface molecules encoded by a large gene family which controls part of the immune system in vertebrates
it is the most polymorphic region known
what is the most polymprphic region of genome known as
the MHC complex
what is the MHC complex primarily involved in
immune system
what is primarily involved in transplant rejection
the major histocompatability complex
what is major function of MHC
bind to peptide fragments derived from pathogens
what is balancing selection
multiple alleles are actively maintained in the gene pool f a pop at frequencies above that of gene muation
usually selects for heterozygotes
what is purifying selection
negative selection
removal of deleterious mutations and can result in stabilising selection through the purging of deleterios variatoin
what is stabilising selection
favours individuals with an intermediate phenotype
what is disruptive selection
favours individuals at both extremes
what is directional selection
favours individuals at one phenotypic extreme
which selection maintains diversity
balancing selection
when does selection change gene frequencies the fastest (wrt. alleles)
when alleles are at intermediate frequencies
