Cycle 6 Flashcards
what is evolution
populations or organisms change over time
what is microevolution
change in allele frequencies that occur from one generation to the next. When these microevolutionary changes occur over a longer period of time they will lead to macroevolution. Ie, the process of evolution.
what is macroevolution
evolution of new species (divergence and speciation)
What happens when there are no evolutionary agents and random mating
This means that the population is not evolving
- allele frequencies do not change
- observed genotype frequencies matches the expected, population is in HWE
what is the Weinberg principle?
Given the observed allele frequencies in a population you can predict the expected genotype frequencies under the scenario of no evolutionary agents and random mating
what are the 5 criteria for hardy Weinberg equilibrium
- no selection
- no mutation
- no immigration or migration (gene flow)
- no genetic drift
- population is randomly mating
- any one violation occurs then evolution can occur
How to calculate HWE
Let p = frequency of one apple Let q = frequency of the second allele * p + q = 1 Math of expected genotype frequencies… p2=f(BB) 2pq=f(BR) q2=f(RR) In HWE expected genotype will match observed genotype
How do you measure selection?
How do you measure the contribution of an individual to future generations?
Fitness: the degree to which an individual contributes offspring (ie. allele frequencies to a future generation)
What is absolute fitness?
- uppercase w
- A mesurable quantity, like # of offspring, sometimes a proxy like the # of surviving offspring, # of eggs, or average lifespan
what is relative fitness?
- the absolute fitness dived by the absolute fitness of the most successful genotype
- w = W/Wmax
- lowercase w
what is selection against the dominant phenotype
- wBB = wBR < wRR
- frequency of the B allele reaches 0
- frequency of the R allele reaches 100
what is selection against the recessive phenotype
- wBB=wBR>wRR
- dominant phenotype will increase approaching 100, but cannot reach fixation
- recessive phenotype decrease but never reaches 0
selection for the heterozygote
- heterozygote advantage
- wHSHSwHNHN
- ex. sickle cell anemia in malaria areas where heterozygote has mild anemia but is resistant to malaria
- ex. corn, heterozygote is the biggest stalk so it is preferred
- allele frequency goes to 0.5-0.5
- maintains genetic variation
- rare alleles increase in frequency and common alleles decrease in frequency
Selection for homozygotes = heterozygote disadvantage (or against heterozygotes)
- wWW>wWS
why does starting allele frequency matter in heterozygote disadvantage?
- rare allele is more likely to be found in the heterozygote
- common allele will be in the homozygous frequent, so it will have the advantage and increase
- results in less genetic variation
- note that for all heterozygote selection it must have a different phenotype than either homozygote (codominance or incomplete dominance)
what is direction selection
- when one extreme is being favoured
- peak of curve at the extreme
what is stabilizing selection?
- When mean phenotype is being favoured and extremes are at the disadvantage
- peak or curve at mean
what is disruptive selection?
- the mean phenotype is at the disadvantage and both extremes are advantages
- peak in curve at both extremes
what is balancing selection?
- (type of section that can happen with heterozygote advantage, and it is the maintenance of variation, so each phenotype is equally favoured)
what is gene flow?
- any movement of individuals or genetic material from one population to another
- ex brown beetle migrates from population 2 to population 1 with only green beetles.
- in population 2, loss of BB results in different proportion of alleles decreasing the genetic variation
- in population 1, the immigration adds the B allele, thus increasing genetic variation
What is genetic drift?
- Change in allele frequency due to the effect of chance
- because not everyone in a population repoducues this results in a change of allele frequency due to this effect of chance
How is genetic drift determined?
- through chance events
- Eg. survival in a storm, some of the birds at the front of the path might die. So if green alleles are in the front, they can get lost.
- In this case only yellow alleles left in population
- Generalized: that since there are fewer rare alleles, they are more likely to get lost
bottleneck effect + the founder effect
the change in allele frequency due to random sampling of a very small # of individuals
- ex. Catastrophic reduction in population = bottleneck effect. Few chance survivors left
- ex. if there is migration to an isolated island there may only be a few founders
- the few founders/chance survivors left reduce allelic variation thus reducing the population’s variation
what are the consequences of genetic drift?
- reduces genetic variability
- which alleles increase or decrease is random
- usually known rare alleles that have. beneficial effect and are actively expressed are more likely to be lost. This results in an increased frequency of deleterious alleles
- small population leads to inbreeding and increased homozygosity
- results in increase of phenotypes with the deleterious traits
- ex cheetahs: malformed sperm, palate erosion, kinked tail
(ie, the expression of deleterious traits)
what is non-random mating?
- individuals select mates based on phenotype
- technically not an evolutionary agent because it does not cause changes in allele frequencies
- Only causes changing genotype frequencies
what is assortative mating?
- like mate with like at one trait
- Ex, white snow geese will mate with white snow geese
what is disassortative mating
- opposite attract, at one trait
- Ex. white striped sparrows also mate tan striped sparrows
inbreeding
- like mates with like genome wide
inbreeding avoidance?
- opposites attract genome wide
what is assortative mating and evolution?
- same phenotypes mating
- you see change in genotype frequency change, therefore the population is not in HWE (AA 250-375, Aa 500-250, aa 250-375), but allele frequency stays the same at 0.5, 0.5 thus no evolution
- can work with selection to cause evolution
- increases homozygosity
what are the consequences of inbreeding?
- increase in homozygosity exposes phenotype of deleterious (harmful) recessive alleles
- Because these negatives alleles are expressed when the recessive alleles are homozygous together
- increase prevalence of these harmful phenotypes
= inbreeding depression - Ex. bulldog, median lifespan of 8.4 years, has heart valve problems cataracts, slipped disks, higher risk cancer, hip dysplasia
what is disassortative mating and evolution?
- Opposites mate
- Different genotype frequency
- Same allele frequency
- increase in heterozygotes
(AA 250-250, Aa 250-625, aa 250-125) - mating between unrelated individuals
= inbreeding avoidance, outcrossing - Can work with selection cause evolution
- Ex. outcrossing results in hybrid vigour in corn
Heterozygote has bigger size, when paired with selection with heterozygote advantage results in change of allele frequency and you can get microevolution
