. In fruit flies white eyes (Xe) is recessive to red eyes (XE) and is sex linked, and hairy body (h) is recessive to hairless (H) and is autosomal. A red-eyed, hairy male is crossed with a red-eyed, hairless female whose father was white-eyed and whose mother was hairy.
a. What are the genotypes of the parents?

b. What proportion of the total offspring will be:
1) Red-eyed and hairy?

2) White-eyed and hairless males?

3) White-eyed and hairless females?

Answer and Explanation:

Available data:

We know that the female is red-eyed and hairless. So its genotype must be XEX- H-. E is the dominant allele for the red eyes color, and H is the dominant allele for the absence of hair. The "-" symbols mean that we do not know yet if it is a dominant allele (in which case the female´s genotype for the trait would be dominant homozygous) or a recessive one (In which case the female´s genotype for the trait would be heterozygous). We must figure it out.

Both female´s parents had to give the female one allele each. This is, the female inherited one allele from each parent. As the father was recessive for the color of the ayes, which is a sex-linked gene, it gave the female the "Xe" allele. And in the same way, as the mother was recessive homozygous for the hair trait, it gave the female the "h" recessive allele.

We also know that the female is red-eyed and hairless, which means that its genotype must include the dominant forms, "XE" and "H", also inherited from the parents. So, if the father gave the female the recessive Xe form, then the mother must have given it the dominant XE form. And in the same way, if the mother gave the female a recessive allele h for hair trait, then the father must have given it the dominant form for the hairless trait, H.

This means that:

Cross: A red-eyed, hairy male is crossed with a red-eyed, hairless female

Parental) XEY hh   x   XEXe Hh

Gametes) XEh   Yh      XEh   Yh   (male)

                XEH   XEh   XeH   Xeh   (female)

Punnet Square)   XEh           XEh             Yh            Yh

              XEH    XEXE Hh    XEXE Hh    XEY Hh     XEY Hh

              XeH    XEXe Hh    XEXe Hh    XeY Hh      XeY Hh

              XEh    XEXE hh     XEXE hh    XEY hh      XEY hh

              Xeh    XEXe hh     XEXe  hh    XeY hh      XeY hh

F1)  6/16 red-eyed and hairless individuals in total

     4/16 red-eyed and hairless females

     2/16 red-eyed and hairless males

     2/16 white-eyed and hairless males

     6/16 red-eyed and hairy individuals in total

     4/16 red-eyed and hairy females

     2/16 red-eyed and hairy males

     2/16 white-eyed and hairy males

    2/16 females are dominant homozygous for the color of the eyes    

    and heterozygous for the hair trait, XEXE Hh  

    2/16 females are heterozygous for both traits, XEXe Hh

    2/16 females are dominant homozygous for the color of the eyes    

    and recessive homozygous for the hair trait, XEXE hh

    2/16 females are heterozygous for the color of the eyes    

    and recessive homozygous for the hair trait, XEXe hh  

   2/16 males are red-eyed and heterozygous for the hair trait, XEY Hh

   2/16 males are white-eyed and heterozygous for the hair trait, XeY

   Hh  

   2/16 males are red-eyed and recessive homozygous for the hair trait, XEY    

   hh

    2/16 males are white-eyed and recessive homozygous for the hair trait,    

    XeY Hh

a. What are the genotypes of the parents?

b. What proportion of the total offspring will be Red-eyed and hairy?

   6/16 red-eyed and hairy individuals in total

   What proportion of the total offspring will be White-eyed and hairless   males?

    2/16 white-eyed and hairless males, XeY Hh

    What proportion of the total offspring will be White-eyed and hairless females?

     0/16 white-eyed and hairless females. All females are red-eyed

the correct answer is d

c. heat from the poles back down towards the equator.