Question

Small populations of flies that had three genotypes/phenotypes for eye color (red,orange, and white) were observed over several generations under laboratory controlled conditions (all the same for the samples). Over time the diversity in many of the populations changed from flies of three colors to flies of one color, inevitably red or white, but never the heterozygous condition of orange. These observations suggest a. Natural Selection, red or white eyes were more adaptive. b. Sexual Selection, the females were not attracted to orange eyes. c. Genetic Drift, fixation happen rapidly in these small populations.

Answer 1

The selection of a particular genotype, be it heterozygous or homozygous all points towards evolution. In this case, the three modes of fixation of alleles given are Natural Selection, Sexual selection, and Genetic Drift. Without any further knowledge about their reproductive patterns, it cannot be assumed that the fixation of either homozygosity is due to sexual selection. Again sexually selected characteristics present would favor only one color and not two.

The remaining choices would be Natural Selection or Genetic drift. Although both lead to fixation of alleles, in natural selection this fixation is of the advantageous trait, i,e a phenotype that confers the most advantage to the organism. It occurs in a large population and the selected trait would give a reproductive advantage. While genetic drift occurs in a small population as a random chance event causing random fixation of alleles. In this question, the laboratory-controlled mating of a small population of flies leads to fixation of either red or white eyes, referring to genetic drift.