Topic 4 (evolution of populations)

Question 1

while the process of selection acts on the _______ (causing differential survival and reproduction), the outcome of natural selection (ie evolution) is manifested at the ________ level

Answer 1

individuals, population

Question 2

what is a gene

Answer 2

a combination of two alleles

- in diploid individuals

Question 3

genetic variation (allelic variety) is determined by:

Answer 3

the diversity of alleles in a population

- often measured by determining proportion of heterozygotes/ or # of alleles at various loci

Question 4

the change in the frequency of alleles in a population (gene pool) between generations

Answer 4

evolution!

- no evolution occurs if allele frequencies don’t change

Question 5

List the 5 factors that can change allele frequency (ir result in evolution)

Answer 5

1. natural selection
2. sexual selection (non-random mating)
3. mutations ( changes in allelic varieties)
4. gene flow
5. genetic drift (affects small populations much more)

Question 6

Does sexual selection (non-random mating) increase or decrease genetic variation generally?

Answer 6

decrease because certain varieties are preferred over others (phenotypes, inbreeding, etc)

Question 7

list the 4 reasons why natural selection cannot fashion perfect organisms

Answer 7

1) selection can act only on existing variations (you can’t create perfect out of nothing!)
2) evolution is limited by historical constraints ie bird teeth, human tailbones
3) adaptations are often compromises. eg) frogs that make loud noises attract more mates, but also attract more predators
4) chance, natural selection, & the environment interact (so advantageous traits are always changing)

Question 8

list the 5 prezygotic isolation mechanisms

Answer 8

1. ecological (habitat) selection/ geographical
2. temporal isolation (different breeding seasons)
3. behavioral isolation (different mating rituals/ attractions)
4. mechanical isolation/ morphological (anatomically incompatible)
5. gamete isolation (sperm and egg cannot fuse)

Question 9

what is selected for/ against in directional selection

Answer 9

one extreme is favored, meaning that the other extreme is selected against

Question 10

what is selected for in disruptive/ diversifying selection?

what does it result in?

Answer 10

both of the extremes. Alleles are not lost if it’s perfectly split down the middle, so genetic variation is maintained.
- results in polymorphism (2 or more divergent phenotypes)

Question 11

What are the 3 ways natural selection can affect the distribution of allele frequencies?

Answer 11

1. directional selection
2. disruptive/ diversifying selection
3. stabilizing selection

Question 12

explain stabilizing selection

Answer 12

common phenotypes are favored (selection against extremes). The population becomes more alike, and there is little or no evolutionary change ( maintains genetic variation). No loss in alleles! (heterozygote)

Question 13

What is negative frequency- dependent selection?

Answer 13

the rare genotype has advantage

- whatever phenotype is more frequent has a fitness disadvantage, so we see a shift in the pop.

Question 14

give an example of heterozygous advantage

Answer 14

sickle cell anemia