Population Genetics: Lect 24 and 25

Question 1

Heterozygote advantage:

Answer 1

• SCA

ex: person w/ sickle cell trait (heterozygotes) are resistant to falciparum malaria.

Question 2

Natural Selection:

Answer 2

• increases the frequency of alleles that promote survival.
• decr. the freq of alleles that reduce survival.
• SC and B-thalassemia trait protected against malaria.

Question 3

Reproductive fitness

Answer 3

• depends on survival to reproductive age and fertility of individual once reprod. age is reached.
• Tay-Sach’s = zero fitness due to death in infancy
• Turner synd = zero fitness due to infertility.
• PKU = reduced fitness if untreated due to intellectual disability or normal if well treated.

Question 4

Genetic Drift:

Answer 4

-the change in the frequency of a gene variant (allele) in a population due to random sampling of organisms.

Question 5

Founders effect

Answer 5

• person w/ a recessive allele of a gene moves into the population; new population w/ higher frequency of the mutant gene.
• coupled to social, religous or geographic isolation results in higher freq. of the mutant allele.
• ex: Tay-Sach’s, Canavan and Gaucher disease more prevalent in Ashkenazi Jews. Higher incidence of albinism in Hopi Indians of Arizona. Ataxia telangiectasia, cystic fibrosis common in the Amish from Holmes County, Ohio

Question 6

Prevalence of mutant allele in high frequency in a population:

Answer 6

• geographical isolation
• natural selection
• higher incidence of consanguinity
• high mutation rates of the gene

Question 7

Assumptions of Hardy-Weinberg Equilibrium

Answer 7

HW is used to estimate the incidence of heterozygous carriers in the population.The incidence of heterozygous carriers is much higher than the incidence of affected homozygotes

•Population islarge
•Random mating between individuals
–No consanguineous mating
–No mate selection based on genotype
•No new mutations in the population
•No migration of individuals into the population

Question 8

Factors causing genetic variation in populations

Answer 8

• New mutation
• Naturalselection
• Genetic drift
• Consanguinity