Genetics Exercise
Directional selection entails natural selection favoring one phenotype causing its allele frequency to shift in one direction. The constant increase in frequency of the favored allele is independent of its dominance compared to other alleles; thus, even recessive alleles can ultimately become fixed. For instance, environment pressures and changes of diet affect the size (depth) of beaks of a population of cardinals in the subsequent generations. During the rainy spells, there is a huge supply of small seeds as compared to large seeds; therefore, the cardinals seldom ate large seeds and their beaks become shorter. Throughout the dry spells, neither the ...
