Population genetics

Question 1

What is population genetics?

Answer 1

quantitative study of distribution of traits in a population and how they change over time

Question 2

What is HW for gene with 2 alleles A and a in population?

Answer 2

p(sq) + 2pq + q(sq) = 1

AA + 2(a)(A) + aa = 1

Question 3

What are the assumptions of HW?

Answer 3

1. random mating
2. allele frequency same in males and females
3. no selection
4. no migration into population
5. no new mutation
6. population large enough that allele frequency doesn’t change over populations

Question 4

How does HW change for multiple alleles? For example, B-hemoglobin has 3 alleles (A, S, C)

Answer 4

(p + q + r)(p + q + r) A = p, S = q, C = r
p(sq) + pq + pr + qp + q(sq) + qr + rp + rq + r(sq)

A(sq) + 2AS + S(sq) + 2AC + C(sq) + 2SR

Question 5

How can Hardy Weinberg apply to disease like PKU and CF with hundreds of mutations implicated in disease?

Answer 5

treat as 2 alleles because variants produce the same phenotype

Question 6

How do you use Hardy Weinberg for X-linked recessive disease?

Answer 6

Males = p + q = 1
Females = p(sq) + 2pq + q(sq) = 1

Question 7

What adjustments to HW do you make for rare autosomal dominant diseases?

Answer 7

Like with Familial hypercholesterolemia, q is basically 1 so use 1 = 2p + p2, where 2p = Hh.

Question 8

What are deviations from random mating?

Answer 8

3 inter-related forms: stratification, assortative mating, inbreeding

Question 9

What is stratification?

Answer 9

population subgroups that remain genetically separate - example - Ashkenazi jews

Question 10

What is assortative mating?

Answer 10

Mating choice based on some trait, positive or negative. Example for neg - deaf marrying deaf, achondroplasia marrying achondroplasia

Question 11

What is Inbreeding

Answer 11

marrying of closely related individuals like Amish

Question 12

What are ethnic diseases?

Answer 12

Caused by stratification. Cystic Fibrosis among caucasians, Sickle cell anemia among African Americans, Tay Sachs among Ashkenazi

Question 13

Does inbreeding increase frequency of allele?

Answer 13

No, just frequency of homozygotes

Question 14

What increases the risk of a rare recessive disease?

Answer 14

Related parents

Question 15

What mutations are favored by selection?

Answer 15

Cystic fibrosis mutation confers resistance to typhoid, sickle cell anemia confers resistance to malaria

Question 16

What patterns of inheritance deviate from Hardy Weinberg?

Answer 16

autosomal dominant and x-linked recessive. If mutation produces genetic lethal, alleles are removed from each generation

Question 17

What is fitness?

Answer 17

probability of transmitting one’s genes to the next generation relative to to the population’s average

Question 18

What reduces fitness to zero?

Answer 18

a mutant allele that is lethal or causing sterility. For example, Cystic Fibrosis reduces male fitness to near zero.

Question 19

What are examples of diseases that deviate from HW and have a fitness near 0.

Answer 19

Dominant mutations - osteogenesis imperfecta, Rett syndrome

X-linked recessive - duchenne muscular dystrophy. All either cause sterility or lethality

Question 20

What is genetic drift?

Answer 20

Allele frequency can fluctuate from generation to generation by chance.

Question 21

What is gene flow?

Answer 21

migration, can cause allele to enter new populations. PKU allele is far more common in Irish, but has entered other parts of Europe though far less in Asia

Question 22

What is founder effect?

Answer 22

when small population separates from a larger population, allele frequencies may be different in that smaller group.

Question 23

What is heterozygote advantage?

Answer 23

Those heterozygous for sickle cell anemia are more likely to survive malaria