How might genotype frequencies of alleles for body size change under directional selection? see section 23.3 ( page 463) ?

The directional selection is the type of natural selection, in which an extreme phenotype is  promoted due to the changes in the environment. This causes the changes in the allele frequency  and the shifting of the phenotype in a particular direction. In this condition, one of the extreme phenotypes are promoted, which result in the shifting of genotypic frequency either of the homozygous characteristics.

answer: the answer is b

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explanation: