Question

The following pathway is proposed to explain the inheritance of purple flower color in pea plants: Colorless Precursor→Colorless Intermediate→Purple Pigment. A dominant allele for Gene C provides an enzyme that converts Colorless Precursor→Colorless Intermediate. A dominant allele for Gene P provides an enzyme that converts Colorless Intermediate→Purple Pigment. An explanation of why plants with CCpp and ccPP genotypes have white petals while plants with the CcPp genotype have purple flowers is?

Answer 1

In pea plants, purple flowers are produced when there is at least one dominant allele for two different genes responsible for flower color. Plants with CCpp or ccPP genotypes have white flowers due to a lack in enzyme production for the purple pigment pathway. A Punnett square analysis for a PpYY and ppYy cross requires 16 squares.

Step-by-step explanation:

The inheritance of purple flower color in pea plants follows a dihybrid cross involving two genes: a gene C and a gene P. The dominant allele C is responsible for converting a colorless precursor to a colorless intermediate, and the dominant allele P converts this intermediate to the purple pigment. Plants with a CcPp genotype have purple flowers because they have at least one dominant allele for each gene, providing the necessary enzymes for both steps in the pigment pathway. However, plants with CCpp or ccPP genotypes display white petals since one of the enzymes is not functional due to the presence of two recessive alleles. This results in a block in the biosynthesis pathway, preventing the formation of purple pigment.

For a cross between genotypes PpYY and ppYy, the possible genotypes for the offspring are PpYy, PpYY, ppYy, and ppYY, and the phenotypes would be purple flowers with yellow peas and white flowers with yellow peas. To analyze this cross with a Punnett Square, you would use 16 squares since each parent can produce four different types of gametes (PY, Py, pY, and py, for PpYY; and pY, py, for ppYy).