Lecture 26

Question 1

Hardy-weinberg equilibrium

Answer 1

p2+2pq+q2
p = normal allele
q = diseased allele

Question 2

difference between genotype and allele frequency

Answer 2

genotype : p, pq, q

allele : p or q (p+q=1)

Question 3

For autosomal recessive disorder, what does q2 mean?

Answer 3

disease incidence

Question 4

What is the assumption that we make for autosomal recessive disorder in regard to small q?

Answer 4

since q is very small number, as long as q is less than 5%, p =1.
So 2pq=2q

Question 5

Risky population for hemochromatosis

Answer 5

celtic

Question 6

risky population for sickle cell disease

Answer 6

african

Question 7

risky population for thalassaemia

Answer 7

asia

Question 8

risky population for cystic fibrosis

Answer 8

nrothern european

Question 9

risky population for tay sachs disease

Answer 9

ashkenazi jewish

Question 10

For X-linked recessive disease, what does q, q2, and 2q mean?

Answer 10

q = incidence in male
q2 = incidence of disease in homozygous females
2q = frequency of heterozygous carrier females

Question 11

For autosomal dominant, how is incidence calculated?

Answer 11

q=1/2I

Question 12

Assumption on hardy-weinberg equilibrium

Answer 12

• Population is large
• random mating (no consanguity, no mate selection)
• no new mutation
• no migration

Question 13

Heterozygote advantage of sickle cell anemia

Answer 13

In a carrier, malaria parasite is more likely to cause rupture of the red blood cell, reducing the ability of plasmodium to proliferate thus providing an advantage to being heterozygous for mutant allele. So heterozygote frequency is high.

Question 14

What is reproductive fitness?

Answer 14

fitness depends on survival to reproductive age and fertility of individual.
EX) Tay-sach’s disease represent zero fitness due to death in infancy. while huntington disease has an average fitness since the person carrying the mutation has produced children

Question 15

What is founder effect?

Answer 15

coupled to social, religous or geographic isolation, recessive mutant allele moves into small population from large population. This will cause spread of recessive allele, eventually giving rise to high frequency of mutant allele in small population.
EX) Tay-sach disease in ashkenazi jewish

Question 16

When the prevalence of a mutant allele is in high frequency in population, what are 4 causes that have to be looked for?

Answer 16

1. Geographical isolation
2. Natural selection (heterozygote advantage & improved fitness)
3. Consanguinity
4. High mutation rates of the gene (hotspot)