If an individual has a dominant phenotype for a trait and produces an offspring with a...

If an individual has a dominant phenotype for a trait and produces an offspring with a recessive phenotype, which of the following is true?

1. We can't determine the genotype of the dominant parent

2. The offspring must have at least one dominant allele

3. The dominant parent is heterozygous

4. The other parent must have the recessive phenotype

Solutions

Expert Solution

3. The dominant parent is heterozygous

Let us consider the genotype of the offspring to be aa as the genotype of the offspring is recessive. In order for the genotype to be recessive, both the alleles should be recessive.

This indicates that the offspring received each of the recessive allele (a) from each of its parents.

Now it is given that one of the parent has a dominant phenotype. But as the offspring recieves one recessive allele from each of its parents, this parent has a heterozygous dominant genotype Aa.

As the offspring recieves the other recessive allele from its other parent, the other parent can have a heterozygous dominant genotype Aa or a homozygous recessive genotype aa.

Let us demonstrate this by Punnett square diagram: heterozygous dominant genotype Aa x heterozygous dominant genotype Aa

Genotype of parents: Aa x Aa

Gametes: A a A a

Genotype of offsprings: AA Aa Aa aa

One of the offsprings has genotype aa.

Let us check another possibility by Punnett square diagram: heterozygous dominant genotype Aa x homozygous recessive genotype aa

Genotype of parents: Aa x aa

Gametes: A a a a

Genotype of offsprings: Aa Aa aa aa

Two of the offsprings have genotype aa.

So the dominant parent has a heterozygous genotype. The other parent can have heterozygous genotype or homozygous recessive genotype.

gladiator answered 1 year ago

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