Lecture 26: Population Genetics and Complex Risk Problems

Question 1

Genotype frequency and allele frequency relationship?

Answer 1

To find genotype:
-Add specific number of alleles together

To find allele number:
-Multiple genotype for a certain allele by 2

Question 2

Hardy Weinberg equation

Answer 2

P^2 + 2pq + q^2 = 1

P + q = 1

P= Dominant/Normal allele
q= Recessive/Mutant allele

2pq= Carriers
P^2= homozygous for normal
q^2= homozygous for disease (disease incident)

Question 3

Autosomal recessive Disorders

Answer 3

q = square root of Incidence for the disease

***If q < 5% (1 in 50) assume P=1, so 2pq ≈ 2q (likelihood of being a carrier of disease is two times greater than the chance of being affected by the disease)

Question 4

Autosomal dominance Allele frequency from Incidence

Answer 4

q= 1/2 x I

Question 5

New mutation

Answer 5

-A balance of new mutations and reduced fitness (loss of mutant allele) stabilizes the mutant gene frequency in the population

Question 6

Sickle Cell DIsease

Answer 6

• Heterozygous advantage against malaria
• Autosomal recessive
• Blood cells shaped differently due to

Question 7

Natural selection definition and Sickle cell

Answer 7

• Increases the frequency of alleles that promote survival
• Decreases the frequency of alleles that reduce survival

Sickle cell:
-High prevalence in Africa because protects against malaria
(B-thalassemia also does this)

Question 8

Reproductive Fitness

Answer 8

Fitness depends on survival to reproductive age and fertility of the individual, once reproductive age is reached

Question 9

Genetic Drift

Answer 9

• Change in the frequency of an existing gene variant in a population
• Fluctuations don’t effect big populations but may fix or extinguish an allele in small populations

Question 10

Founder effect

Answer 10

• Reduction in genetic variation that results when a small subset of a large population
• Founder effect coupled to social, religious or geographic isolation would result in a higher frequency of the mutant allele

Question 11

Consanguinity

Answer 11

• Mating of individuals who are related to one another
• They are more likely to share the same disease causing genes
• Higher incidence of genetic disease in offspring (especially if autosomal recessive)

Question 12

X-linked Recessive DIsease

Answer 12

1 = p + q for men

q = incidence (for X-linked)

Question 13

X-linked Recessive Disease

Answer 13

1 = p + q for men

q = incidence (for X-linked)