You are studying fox snakes in your laboratory and you notice that in your colon

Question

You are studying fox snakes in your laboratory and you notice that in your colony some have dark spots on their back, whereas others do not have those dark spots. From this, you determine that the fox snakes have a gene for scale pigmentation, and that there are two alleles in the population for this gene; one for spots and the other for no spots. In total, you have a total of 30 snakes in your population, 22 have spots and 8 do not have spots. For the purposes of this problem, you can use S = dominant allele and s = the recessive allele.

You grab a spotted snake from problem 1. Unfortunately you do not know its genotype. Fortunately, there is a specific type of cross you can do to determine its genotype.

a. What type of cross would you set up?

b. What would the genotype be of the other snake you would use to set this cross up?

Explanation / Answer

The type of cross required to determine the genotype for the allele would be a test cross, which is a cross between a pair of both homozygous recessive and dominant to obtain heterozygous offsprings. The truly heterozygous snakes are crossed together to get a ratio of the trait, which should be 3:1. The genotypes of the snakes used in the first cross would be SS and ss.

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