Question

Give the genotype of each of the parents in each of the following.

i. A gray, normal male mated with a gray, normal female produce 38 gray normal, 15 gray waltzers, 11 white normal and 4 white waltzers.

ii. A gray, normal male mated with a gray, normal female produce 38 gray normal, 15 gray waltzers, 11 white normal and 4 white waltzers.

iii. A gray, normal male mated with a white, waltzer female produces 8 normal, 7 gray waltzers, 9 white normal and 6 white waltzers.

I would like to check my work :)

Answer 1

i. GGNn x ggNn
ii. GgNn x GnNn
iii. GgNn x ggnn

Answer 2

What a wonderful question. Though haven't you posted the same condition (i) and (ii) twice? Parents are the same, offspring at the same in both crosses?

You know that 'grey' is dominant to 'white' and that 'normal' is dominant to 'waltzer.' You get this from the first two crosses: in the first two crosses, both parents are grey - yet they have some white offspring. Similarly both parents are 'normal' yet they have some offspring with a different phenotype, waltzer, so they must have alleles for waltzer masked by normal alleles.

So I'd say the parent genotypes in (i) and (ii) are both GgNn x GgNn.

Taking the very non conventional notation you have adopted of naming alleles for the dominant phenotype instead of the recessive one. ;)

The third cross is a test cross - when an unknown individual, the male in this case, is mated with an individual who is entirely recessive. The female in this case. If she had a dominant allele for either color or normal/waltzer, she'd exhibit the dominant phenotype and she doesn't. So she is ggnn.

Look at the possibilities for Dad: from his phenotype, he is grey (dominant) and normal (dominant). So he could be either heterozygous or homozygous dominant for both those traits. His possible genotypes are:

GGNN
GgNN
GgNn
GGNn

You know that some of his offspring are white - so they must get a recessive color allele from Dad to go with their recessive color allele from Mom. So he must he heterozygous for Gg. Similarly, some of his offspring are waltzers, so they must have got that recessive allele from him too. So you know he is Nn.

So GgNn x ggnn for the third.

Still puzzled about the (i) and (ii) crosses.