Question

C. Cross a male homozygous black rat with

a female heterozygous rat.
1) genotype=
2) phenotype=

Answer 1

In a cross between a male homozygous black rat and a female heterozygous black rat, all offspring would have a black coat phenotype. The expected genotypic ratio is 1:1 for homozygous black (BB) and heterozygous black (Bb) offspring.

Step-by-step explanation:

Genetics of Rat Coat Color

When crossing a male homozygous black rat with a female heterozygous black rat, the genotype and phenotype can be determined as follows:

1. Genotype: All offspring will receive a black allele from the father (BB) and can receive either a black (B) or white (b) allele from the mother (Bb), leading to genotypes of either BB or Bb.
2. Phenotype: Since black is dominant to white, all the offspring will have a black phenotype, regardless of whether they carry the heterozygous (Bb) or homozygous (BB) genotype.

In test crosses between dominant expressing individuals with an unknown genotype and a homozygous recessive individual, the offspring phenotypes reveal whether the unknown parent is heterozygous or homozygous for the dominant trait.

Overall, the expected outcome would be 100% black-coated rats with a genotype ratio of 1:1 for BB:Bb.