Question

2. a. If you represent the allele frequencies as f(T)=p and f(t)=q, what does the Hardy-Weinberg Equilibrium Model predict the genotype frequencies will be in the rodent population in the next generation (show the calculations)?

      b. What are the assumptions of the Hardy-Weinberg Equilibrium Model?

      c. What does the model predict about the genotype and allele frequencies at generations 10, 100, 1000? (Note: This is where the “Equilibrium” comes from)

      d. So, the H-W Eq. Model is a model of no evolution. It predicts that the genetic composition of a population should remain constant over time IF no forces of evolution (the Assumptions in b. above) are acting in the population. Briefly, what is the use of this model of no evolution in studying evolution at a genetic locus?

Answer 1

Ans. #A. For a population as HW equilibrium, the allelic and genotype frequencies remains constant over generations.

# Hardy- Weinberg Equation for 2 allele system (for a population at HW equilibrium) is given by-

p + q = 1                                                       - equation 1

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

Where,

p = allelic frequency of allele 1 (say, dominant allele T)

q = allelic frequency of allele 2 (say, recessive allele t)

p² = genotypic frequency of homozygous (TT)

q² = genotypic frequency of homozygous (tt)

2pq = genotypic frequency of heterozygote (Tt)

# Given allelic frequencies-             f(T) = p           ; f(t) = q

Now,

            Genotype frequencies are-

            Genotypic frequency of homozygous (TT) = f(T) x f(T) = p x p = p²

            Genotypic frequency of homozygous (tt) = f(t) x f(t) = q x q = q²

            Genotypic frequency of heterozygote (Tt) = 2 x f(T) x f(t) = 2 x p x q = 2pq

#B. The HW equilibrium assumption are-

            1. The population is infinitely large and steady,

            2. All members are fertile and produce equal number of offspring through random mating,

            3. Segregation of alleles during gametogenesis follows Mendelian principles,

            4. Migration does not occur,

            5. Mutation does not occur, and

            6. Natural selection is not in action.

#C. The model predicts that the allelic and genotype frequencies remains constant over generations.

#D. A real population does almost never follows HW equilibrium model. A population at HW equilibrium serves as a hypothetical, ideal population and a negative control for detecting mutation and evolution.

If the allelic and genotype frequencies change over generations in a population, it indicates that the HW equilibrium is NOT maintained constant in the generation. The change in allelic and genotype frequency further indicates that one or more HW assumptions are not obeyed by the population – so, the population has undergone mutations, migration, evolution, etc. over generations at that genetic locus.