1) Consider a population of diploid, sexual organisms. For a given gene there ar

Question

1) Consider a population of diploid, sexual organisms. For a given gene there are two alleles (A and a). The allele frequencies are f(A) 0.8 and f(a)-0.2. What sort of genotype frequencies might you observe if the population were undergoing a notable degree of: i) positive assortative mating iii) heterozygote advantage ii) negative assortative mating 2) Suppose you take a look at a specific population of this species, and survey the genotype numbers on two successive generations: First generation Second generation 159 292 105 150 203 58 a) What is the mean fitness of the population in the first generation? In the second generation? b) How have the allele frequencies changed from the first to the second generations? c) What are the apparent fitnesses of the three genotypes? d) If these fitnesses don't change, what will eventually happen to the genetic make-up of the population?

Explanation / Answer

Q1)a) Postive assortative mating is an increase in the rate of phenotypically similar selective mating compared to what one would observe in natural selection or random mating. Henceforth it is considered a deviation from Hardy-Weinberg principle. It acts as an Evolutionary agent. It has two effects on gene frequency

1) It results in increase in homozygosity. Homozygosity causes gametes to become less variable by increasing frequency of homozygous gametes.

2) It increases total population variability.

Therefore an increase in homozygosity directly increases the gene frequency; so an increased gene frequency is observed.

b)Negative assortative mating :-

Negative assortative mating is a decrease in the rate of phenotypically similar selective mating compared to what one would observe in natural selection or random mating. Henceforth it is considered a deviation from Hardy-Weinberg principle. It acts as an Evolutionary agent. It has two effects on gene frequency.

1) It increases Hetrozygosity.

2) It decreases total population variability.

Therefore it results in a decreased gene frequency.

c) Heterozygote advantage is a condition where an individual pertaining a lethal recessive is benefitted by it's heterozygotic condition compared to a normal individual. This is also known as overdominance. For exmaple: Heterozygote of sickel cell anemia. It maintain gene variation in natural population in face to face selection. However it doesn't have any significant effect on genotype frequency.

Q2a) Genotype frequency of AA= 0.8*0.8 =0.64

Genotype frequency of aa= 0.2*0.2 =0.04

Genotype frequency of Aa= 0.8*0.2 =0.16

Now mean fitness of generation 1 = (0.64*159)+(0.16*292)+(0.04*105)

=152.4

Now mean fitness of generation 2 =(0.64*150)+(0.16*203)+(0.04*58)

= 130.8

b) The allele frequency decreased from first to second generation.

c) Without fitness change natural selection cannot take place and adaption cannot occur. Henceforth the absence of adaption a species cannot pertaine in an enviornment for took long as the ecosystem keeps on evolving and the given species might face different type of competition and adverse climatic conditions so if a species shows constant fitness it might eventually go extinct as they lack the capability of facing the adverse conditions or competition caused by the change in their ecosystem.

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