Question

A gene in a population of sexually reproducing organisms with the following genotype frequencies is at Hardy-Weinberg Equilibrium: BB 100, Bb 800, bb 100

A) true B)false C) can not be determined

Which of the following evolutionary forces would be the best explanation for the genotype frequencies in the population in the above question?

A) genetic drift B) there are no evolutionary forces acting on this gene population C)assortive mating D) Overdominance E)Directional selection

If a population is at Hardy-Weinberg equilibrium, which of the following allele frequencies would yield the smallest number of heterozygotes? A)

A=0.25, B=0.75 B)   A=0.75, B=0.25

C)A=0.50, B=0.50

D)A=0.10, B=0.90

Fixation occurs when one allele becomes the only allele for a gene in a population, meaning that all other alleles for that gene have been lost. True or false

Answer 1

Hardy- Weinberg Equation for 3 allele system (for a population at HW equilibrium)

p + q = 1                                  - equation 1

(p + q)² = p² + q² + 2pq = 1                   - equation 2

Where,

p = allelic frequency of allele P

q = allelic frequency of allele Q

p² = genotypic frequency of PP

q² = genotypic frequency of QQ

2pq = genotypic frequency of PQ

Genotype	Number of individuals	Observed frequency	Expected frequency (using HW equation)	Expected no. of Individuals (expected f x population size)
BB	100	f(B) = (2BB+ 1Bb)/ 1000 = 0.5	f(BB) = (0.5)2 = .025	250
Bb	800		f(Bb) = 2 x 0.5x 0.5 = 0.50	500
bb	100	F(b) = (2bb+ 1Bb)/ 1000 = 0.5	f(bb) = (0.5)2 = .025	200
	Total= 100

X² Test, p value= 000

The population is at HW equilibrium.

Ans. 2. E. Direction selection - the process of reduction of genetic variation of the population by selecting for or against a specific allele, thus shifting predominant traits at either of one extreme.

Rest of the options are not process of natural selection.

Ans. 3. See equation 2 [Assuming A and B be allele]-

Heterozygote frequency = 2 pq

            a. 2x 0.25 x 0.75= 0.375              b. 2x 0.75 x 0.25= 0.375

            c. . 2x 0.5 x 0.5= 0.5                    d. 2x 0.1 x 0.9= 0.18

correct option d.

Ans. 3. True