Based on the observed F1 phenotypes above, what can you conclude about the white and singed mutant alleles?

Question

Table 1. Lab section class data for Drosophila F1 generation.

	White, Singed	Red, Straight	White, Straight	Red, Singed
Male	29	8	4	2
Female	2	39	0	0

Based on the observed F1 phenotypes above, what can you conclude about the white and singed mutant alleles? Indicate your conclusions in Table 2 below.  

1)

	white	singed
Is the mutant allele Dominant or Recessive to the wild-type (+) allele? (0.25 pt)	Dominant        Recessive	Dominant        Recessive
Is the gene located on an autosome or on the X chromosome? (0.25 pt)	Autosome    X chromosome	Autosome    X chromosome

Answer 1

Without knowing the phenotypes of the parents, you can at least determine by quantity alone that the dominant traits are Red and Straight and the recessive are white and singed. Because there are 0 recombinants in the female group you can determine that both the genes for hair and eye color are on the same chromosome (otherwise the 4 possibilities would be more evenly distributed).

Both genes are on the X chromosome as the Male offspring and the female offspring have a large discrepancy favoring different parental genotypes. Since the Father is unable to pass an X chromosome to their son's, but the male children have recombinants while the female children do not the expected F1 genotypes are as follows:

F1 Father has genotype of X chromosome with red eyes and straight bristles with a Y chromosome

F1 Mother has genotype of X chromosome with red eyes and straight bristles with an X chromosome with White eyes and singed bristles (this allows for the recombinant possibilities ONLY in the sons but not the daughters)