What will be the chromosome number of the hybrid of two varieties of a plant with 36 chromosomes in the endosperm cell?

Analyze the question: The question says a plant has 36 chromosomes in its endosperm cell. We need the chromosome number of the hybrid (presumably the normal body/diploid cell of the plant).

Concept: The endosperm is triploid (3n). It forms when one sperm nucleus (n) fuses with the two polar nuclei (n + n) in the embryo sac. So 3n = 36.

Solution:

• 3n = 36
• n = 36 ÷ 3 = 12
• Diploid number (2n) = 2 × 12 = 24

So the hybrid (a normal diploid plant formed by fusion of gametes from the two varieties) has 24 chromosomes in its body cells.

Check against the options:

• A. 12 is the haploid number (n), found in gametes.
• B. 24 is the diploid number (2n), which matches.
• C. 35 does not fit any ploidy level.
• D. 48 would be 4n, which is wrong.

Answer: B (24)

Exam tip: Remember the ploidy of the flowering plant's parts:

• Pollen grain/egg cell: n
• Zygote/embryo/body cells: 2n
• Endosperm: 3n

When given the endosperm number, divide by 3 to get n, then multiply by 2 to get 2n. For example, endosperm 36 gives n = 12 and 2n = 24.