Question

Three characters (flower color, seed color, and pod shape) are considered in a cross between two pea plants: PpYyIi* ppYyii. What fraction of offspring is predicted to be homozygous recessive for at least two of the three characters?

Short answer

The fraction of offspring to be homozygous recessive for at least two of the three characters will be 6 in the total 16 offspring. Thus, it will be 3/8.

Step-by-step solution

Homozygous

Organisms have many alternative forms of genes in their genetic material that are called alleles. When these alleles are found identically in the organism, it is called homozygous for that specific gene contributing to a trait.

In homozygous conditions, both dominant and recessive alleles express completely.

Step 2: Recessive traits

Recessive traits are expressed by an allele when it is in a homozygous condition. It can be masked by the presence of other dominant alleles but persists in heterozygous conditions and express when inherited in homozygous conditions.

Step 3: Fraction of offspring that is homozygous recessive for at least two of the three characters 

Two plants having PpYyIi and ppYyii genotypes are crossed while considering three characters (flower color, seed color, and pod shape). One plant having PpYyIi will produce 8 types of gametes (PYI, PYi, PyI, Pyi, pYI, pYi, pyI, pyi), and another plant having ppYyii will produce 2 types of gametes (pYi and pyi).

Genotypes of offspring after crossing these plants will be PpYYIi, PpYyIi, PpYYii, PpYyii, PpyyIi, Ppyyii, ppYYIi, ppYyIi, ppYYii, ppYyii, ppyyIi, ppyyii.