Question

Choose the correct options from given alternatives.
Directional selection
a. Eliminates uncommon forms of alleles
b. Shift allele frequencies in a steady, consistent direction
c. Favors intermediate forms of a trait
d. Works against adaptive traits

Answer 1

Population genetics is the study of change in the frequencies of allele and genotype in a population. Genetic selection is the process by which certain traits become more prevalent than the other traits. There are three types of genetic selection.

Complete answer:
Darwin first described natural selection in his book Origin of Species. According to natural selection, organisms adapt themselves to new conditions and only the fittest survive. It is done by selectively reproducing changes in the genotype to be suited to the new condition.

Genetic selection is a process by which certain traits become more prevalent than the other traits. Genetic selection is of three types:
• Disruptive selection- causes species to diverge and favors both the extreme traits selected.
• Directive selection- favors one extreme trait.
• Stabilizing selection- favors the average for selected population.

Directive selection, also known as positive selection, is a mode of selection in which extreme traits are favored over the others. It causes allele frequency to shift with time in direction of that trait. It was first described by Charles Darwin. It occurs mostly under environmental changes and also when populations move to new areas with different environments. It allows fast change in allele frequency. It also plays a major role in speciation. The main cause of directive selection is the changing environment.

Examples of Directive Selection:
• Neck of giraffe
• Changed color of moths to be protected against predators
• Antibiotic resistance of bacteria

Hence, the correct answer is option (B).

Note: Artificial selection or selective breeding is selection that is carried out by the intervention of humans unlike in natural selection which occurs naturally. Artificial breeding is the process by which humans selectively develop particular phenotypic traits by choosing which typically animal or plant males and females will sexually reproduce and have offspring together. For example, dog breeding, crop breeding, etc.