BILD 3 Lecture Notes - Lecture 6: Directional Selection, Heterozygote Advantage, Zygosity
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Cystic Fibrosis is an autosomal recessive disease which usually leads to death in the early to mid-20s. Carriers are not affected. The normal allele is F and the disease allele is f. You want to know how strong selection is against the disease allele, and set out to find its selection coefficient (s).
What are the relative fitness of the normal genotypes? (0.5 pt. each, no calculation needed)
ÏFF =
ÏFf =
You find the following data regarding the number of people affected by CF 30 years ago, and today, from genetic tests of US hospital patients. In both years, the sample size was of 1348 individuals chosen at random from the population. It is known that that the mean relative fitness of the 1987 population was 0.919.
Distribution | FF | Ff | ff |
1987 | 661 | 566 | 121 |
2018 | 782 | 489 | 77 |
find the relative fitness of the disease genotype, and the selection coefficient of the disease allele. Show your work and round results to 2 significant figures :
Cats have recently migrated from Malaysia to an uninhabited island in the South China Sea. The gene pool of the migrants includes both alleles for straight (T) and stub (t) tails. You study selection pressures on these cats in the wild, finding the following survivorship in a cohort of 650 kittens.
Phenotype | Straight | Bent | Stub |
Genotype | TT | Tt | tt |
Number of Kittens | 100 | 250 | 300 |
Surviving adults | 70 | 161 | 126 |
a) Calculate survivorship and relative fitness for each genotype
b) Calculate the selection coefficient (s) and degree of dominance (h)
c) Is the population of kittens in Hardy-Weinberg Equilibrium? [Assume that freq. (T) = p and freq. (t) = q].
d) Calculate the average fitness of the population of kittens and of the population of adults.
e) Calculate allele frequencies before (kittens) and after (adults) selection in the next generation. [Assume that freq. (T) = p and freq. (t) = q].
f) Which of the two alleles is deleterious? Justify your answer.