. . Gene flow Movement of genes through gametes or movement of individuals in (immigration) and out (emigration) of a population is referred to as gene flow. Organisms and gametes that enter the population may have new alleles or may bring in existing alleles but in different proportions than those already in the population.
Gene flow can be a strong agent of evolution (Fig . ). Migration aa aa aa aa AA AA AA AA AA Fig . Gene flow Peak shifts in one direction (b) Medium-sized individuals are favoured Number of individuals with phenotype Phenotypes favoured by natural selection Peak gets higher and narrower (a) Two peaks form (c) Fig .
Operation of natural selection on different traits (a) Stabilising (b) Directional and (c) Disruptive XII Std Zoology Chapter XII Std Zoology Chapter Evolution If a population is in Hardy Weinberg equilibrium, the genotype frequency can be estimated by Hardy Weinberg equation. (p + q) = p + 2pq + q p = frequency of AA 2pq= frequency of Aa q = frequency of aa p = . , q = . then, p = ( .
= % Aa q = ( . ) . = % aa Hence the beetle population appears to be in Hardy- Weinberg equilibrium. When the beetles in Hardy- Weinberg equilibrium reproduce, the allele and genotype frequency in the next generation would be: Let’s assume that the frequency of ‘A’ and ‘a’ allele in the pool of gametes that make the next generation would be the same, then there would be no variation in the progeny.
The genotype frequencies of the parent appears in the next generation. (i.e. % AA, % Aa and % aa). If we assume that the beetles mate randomly (selection of male gamete and female gamete in the pool of gametes), the probability of getting the offspring genotype depends on the genotype of the combining parental gametes.