In shadow crab populations males are black or white and fema

In shadow crab populations, males are black or white, and females are black, white, or gray.

a) Explain why females and males have different numbers of phenotypes, and include the locus of the carapace color gene. (3)

b) Predict the outcome of a cross between a gray female crab and a white male crab. (4)

Solution

a) In shadow crabs, males are XY and females are XX.

The locus of carapace color gene resides on the X chromosome.

Black and white color genes exhibit incomplete dominance; so when both genes are present, then the color is grey. In males, only one \'X\' chromosome is there, so, grey color is not possible.

b) Gray female X^bX^w crossed to X^wY

Result: X^bY (black) and X^wY (white) males. Half of the males will be black and the rest half will be white.

X^bX^w (grey) and X^wX^w (white) females. Half of the females will be white, and the rest half will be grey.