Question

Brown hair is dominant over red hair. What will the genotypes and phenotypes of the offspring of a cross between a homozygous brown hair person and a heterozygous brown hair person?

Do the process in five steps.

1.

2.

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4.

5.

Answer 1

The offspring of a cross between a homozygous brown hair person and a heterozygous brown hair person will have the genotypes Bb and the phenotypes brown hair. In the F2 generation, the genotypic ratio will be 1 BB : 2 Bb : 1 bb, and the phenotypic ratio will be 3 brown hair : 1 red hair.

Step-by-step explanation:

The homozygous brown hair person will have the genotype BB, while the heterozygous brown hair person will have the genotype Bb.

In the cross between these two individuals, all of the offspring will be heterozygotes with the genotype Bb.

The phenotypes of the offspring will be brown hair, as brown hair is dominant over red hair.

If these heterozygous offspring are self-crossed, the resulting F2 offspring will have the genotypes BB, Bb, and bb, in a ratio of 1 BB : 2 Bb : 1 bb.

The phenotypic ratio of the F2 offspring will be 3 brown hair : 1 red hair.

Answer 2

1) Firstly, lets sort out the alleles for the dominant and recessive characteristics. The dominant brown allele will be written as B and the recessive red hair allele will be written as b.

2) Lets sort out the genotype of the parents. The parent having homozygous brown coloured hair will carry the alleles BB. The parent carrying the heterozygous brown coloured hair will carry the alleles Bb.

3) The punnet square from these parents will be drawn as follows:

B b

B BB Bb

B BB Bb

4) Now, lets predict the phenotype of the offsprings. The results from the punnet square show that all of the offsprings will have brown coloured hair.

5) The genotype for the children will have 50% chance to be homozygous brown (BB) and 50% chance to be heterozygous brown (Bb).