Cats have a gene on the X chromosome that has two alleles—one that makes the cat black (XB) and one
that makes it orange (XO). If the cat has both alleles, it will express both colors! Cats with both black and
orange are called “tortoiseshell”.
1) This color trait is…
a) Autosomal dominant
b) Autosomal recessive
2) The two alleles demonstrate…
a) Complete dominance b) Incomplete dominance
c) X-linked
c) Co-dominance
3) Write the genotypes that will produce the following phenotypes, then complete the Punnett square (below) to
show a cross between a tortoiseshell female with an orange male:
XO
Phenotypes Genotypes
Orange female:
Orange male:
Black female:
Black male:
Tortoiseshell female:
Tortoiseshell male:
XO XO
Y XO
XB
Y XB
XO XB
Y XO XB
XB
Y XO
Y XB
XO XB
XB XB
Y
XB
4) List each different genotype, their phenotypes, and the probabilities (%) for getting each type of kitten
Cats also have a “spotting” gene that gives it white patches on the face, paws, and chest. A cat that is homozygous
recessive for this gene (ss) will be colored all over with no white patches. If the cat is heterozygous (Ss) for this
gene, it will have smaller white patches compared to a homozygous dominant (SS) cat. Cats that have white,
orange, and black are called “calico”.
5) The white spotting trait is…
a) Autosomal dominant
b) Autosomal recessive
6) The two alleles demonstrate…
a) Complete dominance b) Incomplete dominance
c) X-linked
c) Co-dominance
7) Write the genotypes for each of these phenotypes (use both genes, and ignore the size of the white spotting):
Phenotypes Genotypes
Phenotypes Genotypes
Orange female:
Orange male:
Black female:
Black male:
Tortoiseshell female:
Tortoiseshell male:
ss XO XO
ss Y XO
ss XB
ss Y XB
ss XO XB
ss Y XO XB
Orange & white female:
Orange & white male:
Black & white female:
Black & white male:
Calico female:
Calico male:
S_ XO XO
S_ Y XO
S_ XB
S_ Y XB
S_ XO XB
S_ Y XO XB
(the above can be SS or Ss)
8) Complete the Punnett square for the dihybrid cross between the black & white male and the calico female.
SY
SY
SXB
SXB
SS XO Y
SS XO Y
SS XO XB
SS XO XB
SS XO Y
SS XO Y
SS XO XB
SS XO XB
SS XB Y
SS XB Y
SS XB XB
SS XB XB
SS XB Y
SS XB Y
SS XB XB
SS XB XB
SXO
SXO
SXB
SXB
9) What is the genotypic ratio (list all possible genotypes and count them)?
4 SS XO Y : 4 SS XO XB : 4 SS XB Y : 4 SS XB XB
(if you used Ss instead of SS, there will be 8 genotypes with 2 of each)
10) What is the phenotypic ratio (list all possible phenotypes and count them)?
4 Orange/white male : 4 Calico female : 4 Black/white male : 4 Black/white female
(if you used Ss instead of SS, there will be 8 phenotypes with 2 of each)
11) What fraction (out of 16) of the kittens are calico female?
4/16 (if you used Ss instead of SS, there will still be 4 calico, but 2 will have big white spots, and 2 will have
small white spots)