Below is a simplified schematic representation of some of the genetic elements involved in the regulation of Pitx1 gene expression. The large grey rectangle represents the protein-coding region of the Pitx1 gene. The smaller rectangles to the left (b and c) are regulatory switches; each one allows a specific binding protein to interact with it and turn on the Pitx1 gene in a particular tissue. When expressed, the Pitx1 gene is transcribed and then translated to generate the Pitx1 protein. A deletion at the location (a) causes a frameshift mutation.

a) How likely is it that a functional Pitx1 protein would be produced in the jaw?

b) How likely is it that a functional Pitx1 protein would be produced in the pelvis?

(answer likely or not likely for each)

c) Justify your answer in 2-3 sentences.

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.