The gene encoding for body color in zombie flies is "X-Linked". Gray bodies are the wild-type trait and blue bodies are caused by a mutation.
A: Set up a cross between a male with a blue body and a female who is homozygous dominant for a gray body. Indicate the genotypes AND phenotypes of the offspring.
B: Set up the reciprocal cross and indicate the genotypes AND phenotypes of the offspring.
Note: Please use wild-type/mutant nomenclature.
To answer the question, let's understand the X-linked inheritance pattern in this scenario. In fruit flies (Drosophila melanogaster), the gene encoding for body color is located on the X chromosome. The X chromosome is one of the two sex chromosomes, with females having two X chromosomes (XX) and males having one X and one Y chromosome (XY).
A: Cross between a male with a blue body (XbY) and a female who is homozygous dominant for a gray body (XGXG).
To determine the genotypes and phenotypes of the offspring, we need to consider the inheritance pattern:
- Since the female is homozygous dominant (XGXG), all her eggs will contain an X chromosome with the dominant gray body allele.
- The male has a blue body allele on his X chromosome (XbY).
In this cross, the potential genotypes and phenotypes of the offspring are as follows:
- Female offspring (XGXG): They inherit one X chromosome from the male (XG) and one X chromosome from the female (XG). These female offspring will have a gray body phenotype.
- Male offspring (XbY): They inherit one X chromosome from the female (XG) and the Y chromosome from the male (Y). These male offspring will have a blue body phenotype.
B: Reciprocal cross, i.e., cross between a male homozygous for gray body (XGXG) and a female with a blue body (XbXb).
To determine the genotypes and phenotypes of the offspring in the reciprocal cross, we need to consider the same inheritance pattern:
- The male is homozygous for the dominant gray body allele (XGXG).
- The female has a blue body allele on both of her X chromosomes (XbXb).
In this cross, the potential genotypes and phenotypes of the offspring are as follows:
- Female offspring (XGXG): They inherit one X chromosome from the male (XG) and one X chromosome from the female (Xb). These female offspring will have a gray body phenotype.
- Male offspring (XbY): They inherit one X chromosome from the female (Xb) and the Y chromosome from the male (Y). These male offspring will have a blue body phenotype.
To summarize:
A: Cross: Male (XbY, blue body) x Female (XGXG, gray body)
Offspring: Female (XGXG, gray body) and Male (XbY, blue body)
B: Reciprocal cross: Male (XGXG, gray body) x Female (XbXb, blue body)
Offspring: Female (XGXG, gray body) and Male (XbY, blue body)