In a plant, black seed color (BB/bb) is dominant, over white seed color (bb). In order to find out the genotype of the black seed plant, which of the following genotype will you cross it?
Answer: (A) bb. Answer: (A) bb Solution: A black-seeded plant showing the dominant phenotype could be either homozygous (BB) or heterozygous (Bb).
- A.bb✓
- B.Bb
- C.BB/Bb
- D.BB
Correct Answer
(A) bb
Solution & Explanation
Answer: (A) bb Solution: A black-seeded plant showing the dominant phenotype could be either homozygous (BB) or heterozygous (Bb). To determine its genotype, it must be crossed with the homozygous recessive (white, bb) parent in a test cross; the offspring ratio then reveals the unknown genotype. Hence the correct cross is with bb. NCERT Reference: NCERT Class XII, Ch 4, p.58, lines 31-36: "to determine the genotype of a tall plant at F2, Mendel crossed the tall plant from F2 with a dwarf plant. This he called a test cross. In a typical test cross an organism ... showing a dominant phenotype ... is crossed with the recessive parent"