Question

Phenotypes Genotypes
Full color CC, CCch, CCh, CCa
Chinchilla CchCch
Light gray CchCh, CchCa
Himalaya ChCh, ChCa
Albino CaCa

A test cross is performed with light gray rabbit, and the following offspring are noted: five Himalayan color rabbits and five light gray rabbits. Indicate the genotype of the light-gray rabbit.

Answer 1

I am having trouble figuring out what the alleles and genes are. Three alleles - C, Ch and Ca - of one gene...?

Answer 2

Yes that's one gene. The coma separates each gene.

Answer 3

So if it is one gene of three alleles, the possibilities look like this...

I am still having trouble interpreting this question. It seems that in some of your possible genotypes you have told us that the organism has three different alleles when it cannot have more than two. For others you have also shown the same genotype giving different phenotypes which is not possible...

:/

Answer 4

Are the alleles named:

C, Cch, Ch and Ca?

In which case you have four, not three...

Answer 5

And the phenotypes and genotypes are:

Full color: C C; C Cch; C Ch; C Ca
Chinchilla Cch Cch
Light gray Cch Ch, Cch Ca
Himalaya Ch Ch, Ch Ca
Albino Ca Ca

A little clearer with the alleles separated by spaces to indicate that they are indeed on separate chromosomes.

OK, the question is about the dominance/recessiveness relationships between the four of them - which is dominant over which.

Whenever the C appears, it confers a full color coat. So right away we suspect that it is dominant over all the other alleles. Similarly, only when Ca appears with another Ca do see the fully recessive phenotype, so we assume that it is recessive to all other alleles.

C > ? > ? > Ca

The remaining question is whether Cch is dominant or recessive to Ch. The Himalaya rabbits have Ch Ch but the light grey rabbits have Cch Ch. A single Cch allele hides the Ch Ch phenotype; therefore, we have that Cch is dominant to Ch.

C > Cch > Ch > Ca

Now the question tells you that a light grey rabbit is crossed with an albino (i.e., fully recessive) rabbit. There are two possible genotypes for the light grey rabbit but only one phenotype for the albino rabbit:

Possibility 1: Cch Ch x Ca Ca --> 1/2 Cch Ca and 1/2 Ch Ca
Possibility 2: Cch Ca x Ca Ca --> 1/2 Cch Ca and 1/2 Ca Ca

The first possibility gives you 1/2 light grey and one half Himalaya rabbits.
The second possibility gives you 1/2 light grey and one half albino rabbits.

The first option is the one consistent with the given info about the offspring, so you know the grey parent's genotype was Cch Ch.

Hope that's helpful.