Question

An albino corn snake is crossed with a normal-colored corn snake. The offspring are all normal-colored. When these first- generation progeny snakes are crossed among themselves, they produce 32 normal-colored snakes and 10 albino snakes. a. How do you know that only a single gene is responsible for the color differences between these snakes? b. Which of these phenotypes is controlled by the dominant allele? c. A normal-colored female snake is involved in a test-cross. This cross produces 10 normal-colored and 11 albino offspring. What are the genotypes of the parents and the offspring?

Answer 1

a. We can infer that only one gene is responsible for the only two phenotypes of snakes due to the 3: 1 Mendelian ratio. If there were other genes involved, the ratio would be different.

b. The normal-colored

c. To have raised an albino half offspring, these individuals received a recessive gene from both father and mother. And the other half of normal individuals received at least one dominant gene. Since the statement says that the female snake is a normal phenotype, we know that it has a dominant and a recessive gene. The male snake can only be recessive homozygous to generate offspring half and half. If he was heterozygous for the disease, the offspring would have a 3: 1 ratio.

Here you can see the cross and the genotype of each individual:

      A   x  a

a   Aa       aa

a   Aa       aa