Lecture 12

Question 1

what happens if populations are kept small generation after generation?

Answer 1

inbreeding INCREASES with each generation of small population

Question 2

how does habitat fragmentation affect genetic diversity?

Answer 2

each fragment acts as an independent population so genetic diversity is lost and there’s increased inbreeding

Question 3

what is the extinction vortex?

Answer 3

small populations will continue to get smaller and smaller –> the results of being small (reduced fitness and reproduction, etc.) will cause them to be even more small

Question 4

models of natural selection let us predict: (3)

Answer 4

A. final outcome –> allele frequency at locus at eqb
B. rate of evolutionary change –> rate of change in allele frequency at a locus
C. interaction of selection w drift/migration/mutation and how this affects allele frequency

Question 5

what drives natural selection?

Answer 5

ONLY the environment –> no intrinsic factor

Question 6

what does natural selection favour?

Answer 6

favours the highest RELATIVE FITNESS in specific environment

Question 7

how do you calculate relative fitness?

Answer 7

genotypes with the highest absolute fitness are 1

genotypes with lower absolute fitness is numerator and highest absolute fitness is denominator

Question 8

what is the selection coefficient, s?

Answer 8

percent decline in fitness

1 - relative fitness

Question 9

how do you find allelic frequency in next generation affected by natural selection?

Answer 9

1. find genotype frequencies at fertilization
2. find genotype frequencies after selection (using relative fitness and avg relative fitness)
3. find allelic frequency using the new genotype frequencies

Question 10

is natural selection more or less effective in rare recessive alleles? why?

Answer 10

selection is LESS effective in rare recessive alleles

most of the recessive allele will be found in heterozygotes so selection is less effective

Question 11

as population becomes more fit, what do dominant and recessive allele frequencies approach? what type of selection is this?

Answer 11

recessive allele frequency approaches 0

dominant allele frequency approaches 1

this is DIRECTIONAL selection

Question 12

what is balancing selection?

Answer 12

heterozygote has highest advantage

Question 13

describe balancing selection in sickle cell anemia and the relative fitness for each genotype

Answer 13

AA –> susceptible to malaria but no sickle cell disease (w < 1)

Aa –> cell sickles enough so malaria cannot properly infect and only has mild disease (w = 1)

aa –> resistant to malaria but has fatal sickle cell disease (w < 1)

Question 14

why is sickle cell anemia an example of balancing selection?

Answer 14

A and a alleles are maintained and not driven out of the population

Question 15

what is the name of another type of balancing selection that is seen in flowers?

Answer 15

negative frequency-dependent selection

Question 16

how does negative frequency-dependent selection work?

Answer 16

• flower colour polymorphism gives 2 colours
• pollinators prefer whichever colour is more rare
• therefore, an advantage to being rare and flower can maintain both alleles

Question 17

describe why CFTR deleterious mutation is maintained in the population

Answer 17

SELECTION selects against the deleterious variant but MUTATIONS are always occurring to bring back the variant

therefore, decreased by selection but increased by mutation