Hardy-Weinberg Equilibrium: Selection

Question 1

what is a population

Answer 1

a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring

Question 2

what is population genetics

Answer 2

Darwin’s evolution and Mendel genetics ideas combined

Question 3

population genetics - what is the goal

Answer 3

• track the fate, across generations, of genes in a population
• want to know whether a particular allele or genotype will become more common or less common over time, and why

Question 4

define incomplete dominance

Answer 4

homozygotes have intermediate phenotypes

Question 5

define pleiotropy

Answer 5

one gene affects multiple traits

Question 6

define epistasis

Answer 6

one gene affects another

Question 7

define polygenic inheritance

Answer 7

multiple genes affect one trait

Question 8

what is the equation to explain allele frequencies

Answer 8

• p + q = 1
• they are in genetic equilibrium

Question 9

what is the equation to explain genotype frequencies

Answer 9

p^2 + 2pq + q^2 = 1

Question 10

allele frequencies - explain the variable

Answer 10

• p = frequency of dominant allele (A)
• q = frequency of recessive allele (a)

Question 11

genotype frequencies - explain the variables

Answer 11

• p^2 = frequency of homozygous dominant (AA)
• 2pq = frequency of heterozygote (Aa)
• q^2 = frequency of homozygous recessive (aa)

Question 12

what is Hardy-Weinberg (H-W)

Answer 12

• a null model
• describes what we expect to see in a population that is not evolving at a particular locus

Question 13

Hard-Weinberg Equilibrium (H-W E)

Answer 13

• genotype equation is true
• and meets 5 assumptions
• means allele and genotype frequencies remain constant through generations

Question 14

H-W E assumptions

Answer 14

1. no selection
2. no mutation
3. no gene flow/no migration
4. no chance events/drift
5. random mating

Question 15

H-W E assumptions - when can selection happen

Answer 15

can happen anytime but usually between birth and adulthood

Question 16

H-W E assumptions - when can mutation happen

Answer 16

can happen during gamete formation during meiosis

Question 17

H-W E assumptions - when can migration happen

Answer 17

anytime but often just before or after adulthood, one sex disperses

Question 18

H-W E assumptions - when can genetic drift happen

Answer 18

any time but most often describes small population sizes when blind chance allows gametes with same genotypes to participate in more fertilizations than gametes of other genotypes

Question 19

H-W E assumptions - which are mechanisms of evolution

Answer 19

• selection
• mutation
• migration/gene flow
• genetic drift/chance events
• nonrandom mating - not technically a mechanism

Question 20

H-W E - what are the two conclusions

Answer 20

1. allele frequencies in a population will not change over generations
2. p^2 + 2pq + q^2 = 1

Question 21

how would you determine if a population is in H-W E?

Answer 21

1. start with genotype of gen 1 (calculate each)
2. move to allele frequencies
3. figure out what the next generation will be
4. compare with next generation and see if there are differences. if none = in H-W E

Question 22

when the rate of evolution is affected by dominance and allele frequency, what is the outcome

Answer 22

• recessive allele is common = evolution by natural selection is rapid
• recessive allele is rare = evolution by natural selection is slow

Question 23

rate of evolution is affected by dominance and allele frequency - what is an example

Answer 23

Dawson’s flour beetle experiment

Question 24

explain Dawson’s flour beetle experiment

Answer 24

• a gene with two alleles (+/-) were identified
• genotypes +/+ and +/l are normal
• genotypes l/l do not survive (recessive lethal allele)
• started w two experimental populations with all +/l individuals

Question 25

Dawson's flour beetle experiment - explain the change of the alleles

Answer 25

- viable dominant + allele: increases overtime - lethal recessive l allele: decreases overtime

Question 26

define overdominance

Answer 26

when heterozygotes have a higher fitness than homozygous

Question 27

what does it mean for an allele to be fixed?

Answer 27

- there are no other variants for that allele - two allele frequency lines on a graph will not be linear

Question 28

when overdominance is seen, what is the outcome

Answer 28

natural selection will produce equilibrium allele frequencies and fixation will not occur

Question 29

when overdominance is seen - what is an example

Answer 29

Sickle cell and Mukai and Burdick fruit fly experiment

Question 30

explain the Sickle cell and Mukai and Burdick fruit fly experiment

Answer 30

both alleles meet at a certain number (no fixation)

Question 31

define underdominance

Answer 31

homozygotes have higher fitness than heterozygotes

Question 32

when underdominance is seen, what is the outcome

Answer 32

natural selection will fix one allele or the other depending on which is more common

Question 33

when underdominance is seen - what is an example

Answer 33

Foster et al. fruit fly experiment

Question 34

explain the Foster et al. fruit fly experiment

Answer 34

- 2 alleles goes to fixation - starting frequency affects which one becomes fixed

Question 35

what happens when a rare genotype becomes more common than the common genotype, what is the outcome

Answer 35

- negative frequency-dependent selection - natural selection will produce equilibrium allele frequencies and fixation will not occur

Question 36

a rare genotype becomes more common than the common genotype - what is an example

Answer 36

Gigord et al. orchid experiment

Question 37

explain the Gigord et al. orchid experiment

Answer 37

- when yellow trait is rare, it has a higher fitness - when it is common, it has lower fitness - frequency of yellow morph and reproductive success has a neg. correlation