Cycle 6

Question 1

what is evolution

Answer 1

populations or organisms change over time

Question 2

what is microevolution

Answer 2

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.

Question 3

what is macroevolution

Answer 3

evolution of new species (divergence and speciation)

Question 4

What happens when there are no evolutionary agents and random mating

Answer 4

This means that the population is not evolving

• allele frequencies do not change
• observed genotype frequencies matches the expected, population is in HWE

Question 5

what is the Weinberg principle?

Answer 5

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

Question 6

what are the 5 criteria for hardy Weinberg equilibrium

Answer 6

• 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

Question 7

How to calculate HWE

Answer 7

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

Question 8

How do you measure selection?

How do you measure the contribution of an individual to future generations?

Answer 8

Fitness: the degree to which an individual contributes offspring (ie. allele frequencies to a future generation)

Question 9

What is absolute fitness?

Answer 9

• uppercase w
• A mesurable quantity, like # of offspring, sometimes a proxy like the # of surviving offspring, # of eggs, or average lifespan

Question 10

what is relative fitness?

Answer 10

• the absolute fitness dived by the absolute fitness of the most successful genotype
• w = W/Wmax
• lowercase w

Question 11

what is selection against the dominant phenotype

Answer 11

• wBB = wBR < wRR
• frequency of the B allele reaches 0
• frequency of the R allele reaches 100

Question 12

what is selection against the recessive phenotype

Answer 12

• wBB=wBR>wRR
• dominant phenotype will increase approaching 100, but cannot reach fixation
• recessive phenotype decrease but never reaches 0

Question 13

selection for the heterozygote

Answer 13

• 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

Question 14

Selection for homozygotes = heterozygote disadvantage (or against heterozygotes)

Answer 14

• wWW>wWS

Question 15

why does starting allele frequency matter in heterozygote disadvantage?

Answer 15

• 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)

Question 16

what is direction selection

Answer 16

• when one extreme is being favoured

- peak of curve at the extreme

Question 17

what is stabilizing selection?

Answer 17

• When mean phenotype is being favoured and extremes are at the disadvantage
• peak or curve at mean

Question 18

what is disruptive selection?

Answer 18

• the mean phenotype is at the disadvantage and both extremes are advantages
• peak in curve at both extremes

Question 19

what is balancing selection?

Answer 19

• (type of section that can happen with heterozygote advantage, and it is the maintenance of variation, so each phenotype is equally favoured)

Question 20

what is gene flow?

Answer 20

• 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

Question 21

What is genetic drift?

Answer 21

• 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

Question 22

How is genetic drift determined?

Answer 22

• 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

Question 23

bottleneck effect + the founder effect

Answer 23

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

Question 24

what are the consequences of genetic drift?

Answer 24

• 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)

Question 25

what is non-random mating?

Answer 25

• 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

Question 26

what is assortative mating?

Answer 26

• like mate with like at one trait

- Ex, white snow geese will mate with white snow geese

Question 27

what is disassortative mating

Answer 27

• opposite attract, at one trait

- Ex. white striped sparrows also mate tan striped sparrows

Question 28

inbreeding

Answer 28

• like mates with like genome wide

Question 29

inbreeding avoidance?

Answer 29

• opposites attract genome wide

Question 30

what is assortative mating and evolution?

Answer 30

• 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

Question 31

what are the consequences of inbreeding?

Answer 31

• 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

Question 32

what is disassortative mating and evolution?

Answer 32

• 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