Question

A species of salamander has two tail length phenotypes. Short tails are completely dominant over long tails. A scientists crosses a short tailed individual of an unknown genotype with a homozygous recessive individual. Select the answer that correctly describes the potential outcomes of this cross.A. None of the answer options is correct.B. If all of the offspring are short-tailed, the unknown individual is the heterozygous genotype.C. If half the offspring are the recessive phenotype and half are the dominant phenotype, the unknown individual is the homozygous dominant genotype.D. If all of the offspring are short-tailed, the unknown individual is the homozygous dominant genotype.

Answer 1

Answer:

D. If all of the offspring are short-tailed, the unknown individual is the homozygous dominant genotype.

Explanation:

The short tail phenotype is completely dominant over the long tail phenotype. When a short tailed salamander with unknown genotype is crossed with a homozygous recessive long tailed salamander, the cross is called testcross. Lets assume that the allele "S" gives "short tail" phenotype while the allele "s" gives "long tail" phenotype.

If the "short tailed salamander" with unknown genotype is homozygous dominant (SS), the process of the testcross will express only dominant trait (cross 1). On the other hand, if the "short tailed salamander" with unknown genotype is heterozygous dominant (Ss), segregation of alleles during gamete formation would form two types of gametes (cross 2). The 50% progeny would express the "long tail" phenotype while rest 50% will express the "short tail" phenotype.