A parent that is heterozygous for a trait is crossed with a parent that is homozygous recessive for the same trait, as shown in the Punnett square. What is the probability that the offspring will be homozygous dominant for this trait?

There is no punnet square attached but generally none of the offsprings from this cross will be homozygous dominant. The answer is 0.

Explanation:

The question illustrates a single trait encoded by a single gene. According to Mendel, a gene comes in two alternative forms called ALLELES. Each allele encodes different characters of the same gene. For example, let's use the trait for height encoded by a certain gene that has alleles T for tallness and t for shortness. T is dominant over t, meaning that T (tallness) will always mask the phenotypic expression of t (shortness) in a heterozygous state.

A heterozygous parent contains different alleles of the same gene i.e. Tt in this case. However, due to the dominance of allele T (tallness) over allele t (shortness), the tall trait will be expressed. On the other hand, a homozygous recessive parent contains the same alleles for the recessive trait i.e. tt

Using a punnet square, a cross between a heterozygous (Tt) parent and a homozygous recessive parent (tt) will produce offsprings with genotypes: Tt and tt in a 1:1 proportion.

Tt is heterozygous dominant

tt is homozygous recessive

None of the offsprings are homozygous dominant (TT), hence, the probability of producing a homozygous dominant offspring is 0.

t t

T Tt Tt

t tt tt