Question

1. Let's suppose that a gene affecting pigmentation is found on the X chromosome (in mammals or insects) or the Z chromosome (in birds) but not on the Y or W chromosome. It is found on an autosome in bees. This gene exists in two alleles, D (dark), which is dominant to d (light). What would be the phenotypic results of crosses between a true-breeding dark female and a true-breeding light male, and the reciprocal crosses involving a true breeding light female and a true-breeding dark male, in the following species

Answer 1

Note: The question is not complete. The following species are:

1. Birds

2. Drosophila

3. Bees

4. Human

Answer and Explanation:

1. BIRDS

Birds have Z-W breeding system, males being ZZ and females being ZW

Cross 1: true-breeding dark female and a true-breeding light male

Parental) ZDW x ZdZd

F1) 1/2 = 50% of the progeny will be dark, ZDZd (males)

1/2 = 50% of the progeny will be light, ZdW (Females)

Cross 2: true-breeding light female and a true-breeding dark male

Parental) ZdW x ZDZD

F1) 100% of the progeny will be dark, ZDZd + ZDW (both sexes)

2. DROSOPHILA

They have the X-Y system, so

Cross 1: true-breeding dark female and a true-breeding light male

Parental) XDXD x XdY

F1) 100% of the progeny will be dark, XDXd + XDY

Cross 2: true-breeding light female and a true-breeding dark male

Parental) XdXd x XDY

F1) 50% of the progeny will be dark, XDXd (Females)

50% of the progeny will be light, XdY (Males)

3. BEES

Haplo-diploid system

Cross 1: true-breeding dark female and a true-breeding light male

Parental) DD x d

F1) 100% Dark individuals

Cross 2: true-breeding light female and a true-breeding dark male

Parental) dd x D

F1) 50% of the progeny will be dark, Dd (females)

50% of the progeny will be light, d (males)

4. HUMAN

X-Y System

Cross 1: true-breeding dark female and a true-breeding light male

Parental) XDXD x XdY

F1) 100 % of the progeny will be dark, XDXd + XDY

Cross 2: true-breeding light female and a true-breeding dark male

Parental) XdXd x XDY

F1) 50% of the progeny will be dark, XDXd

50% of the progeny will be light, XdY