Q51.3-2CC - Campbell Biology

Question

Balancing selection can maintain variation at a locus (see Concept 23.4). Based on the foraging experiments described in this chapter, devise a simple hypothesis to explain the presence of both for R and s alleles in natural fly populations.

Step-by-Step Solution

Answer

The hypothesis explains the selective advantage to the rover and sitters due to fluctuating population density.

Step 1: Flies

The large numbers of winged insects found almost everywhere, like on ceilings, around pet food, on walls, in trash bins, and around light sources necessary to maintain ecological balance by decomposing organic waste, are called flies.

Examples of flies include horse-fly, mosquitoes, Nematocera, hoverflies, robber flies, black fly, picture-winged flies, tachinid flies, botflies, and flesh fly. The flies' physical features are single pair of wings, two hair pads on three pairs of legs, compound eyes, sponge-like mouthparts, and a moveable head.

Step 2: Balancing selection

The selective process that is considered a form of natural selection in which two or more alleles (genes alternative forms) are maintained in a gene pool is called balancing selection.

Sickle cell anemia is an example of balancing selection due to inheritance from both father and mother mutated genes. 

Step 3: Hypothesis based on the presence of alleles

The balancing selection maintains genetic variation through the maintenance of multiple alleles present at the gene's locus. When the population density of foraging alleles located on a locus is altered over time in generations, either rover or sitter carrying different alleles will be benefited.

The energy-conserving sitter larvae bearing S allele will get benefitted when there is a lower population density. In contrast, the R allele present in mobile Rover larvae of the fly population will become advantageous when the population density is higher.