Complementary Genes.

When two strains of white-flowered Pea plants were crossed, all the flowers of F1 plants appeared pink. In F2 the flowers produced were 9 pink : 7 white.

This indicates the presence of two pairs of genes that control the flower colour characteristic.

If the dominant gene in one pair is represented by A

And the recessive gene in that pair is represented a

While the dominant gene in the second pair is represented by B

And the recessive gene in that pair is represented by b

The genotypes of the white-flowered pea plants (P1) would be (AAbb) and (aaBB). Then the genotype of F1 plants will be (AaBb) as follows:

White-flowered pea plant White-flowered pea plant

Of the 1^st. strain of the 2^nd. strain

P1 AAbb X aaBB

G1

F1 AaBb

Pink-flowered