Question

For any gene with a dominant allele Aand recessive allele a, what proportions of the offspring from an AA*Aacross are expected to be homozygous dominant, homozygous recessive, and heterozygous?

Short answer

For a gene with a dominant allele Aand recessive allele a,no homozygous recessive progenies will be produced from the cross between AA and Aa. 2 out of 4 means ½ offspring will be homozygous dominant and 2 out of 4 means ½ offspring will be heterozygous.

Step-by-step solution

Heterozygous

Heterozygous is the condition of an organism or cell when it contains different alleles for a particular trait. These alleles are transferred from the parents to their progenies.

For example, a tall pea plant is heterozygous when it contains both alleles that show tall and dwarf. In contrast to this, a homozygous tall plant of pea will contain both alleles of tallness.

Step 2: Dominant and recessive allele

In organisms, genes for a character are found in many alternative forms called alleles that are either dominant or recessive on the basis of expressivity.

Dominant alleles always show their effect if they are present in the genotype, either in homozygous or heterozygous conditions. Recessive alleles give their effect only in homozygous conditions.

Step 2: Proportions of the offspring from a homozygous dominant and a heterozygous cross

According to the given case, the genotypes of individuals are AA and Aa and they are crossed. The gametes produced will be A and a. So when these gametes are crossed, offspring will be homozygous dominant (AA) and heterozygous (Aa) and each will be produced in the proportion of ½.