Question

Assuming complete dominance, a phenotypic ratio of ________ is expected from a monohybrid sib or self-cross. A) 1:1 B) 2:1 C) 3:1 D) 5:2 E) 3:2

Answer 1

Answer:

C (3:1)

Explanation:

Gregor Mendel was able to portray complete dominance of an allele over another when he crossed two purebreeding plants; one homozygous for red flowers and the other for white flowers. He discovered that all the F1 offsprings were red-flowered. Hence, he came up with his law of dominance.

He self-crossed the F1 offsprings which were all hybrids or heterozygous i.e. contained a combined allele in their genotype. He discovered that the offsprings produced a phenotypic ratio of 3:1 i.e 3 red-flowered plants to 1 white-flowered plant

The red-flowered plants have genotypes RR, Rr and Rr respectively while the white-flowered plant have a rr genotype.