Question

In apple, the chromosome number of gametes is 17. What is the chromosome number in its Primary Endosperm Nucleus (PEN)?

• A. 34
• B. 68
• C. 17
• D. 51

Answer 1

The Correct Option is D

In apple (Malus domestica), the chromosome number of gametes (n) is given as 17. To determine the chromosome number in the Primary Endosperm Nucleus (PEN), we must understand the process of double fertilization in angiosperms:

1. The PEN is formed through the fusion of: - One male gamete (n = 17) - Two polar nuclei (n + n = 17 + 17 = 34)

2. This results in a triploid nucleus with chromosome number: n + 2n = 17 + 34 = 51

3. The PEN subsequently develops into the endosperm, which is triploid (3n) in most angiosperms including apple.

Thus, the correct answer is (D) 51.

Answer 2

In apple, the gametes have a haploid chromosome number of 17 (n=17). The PEN is formed through triple fusion involving two polar nuclei (each n=17) and one sperm nucleus (n=17), resulting in a triploid nucleus with 51 chromosomes (3n=51). 

This triploid endosperm serves to nourish the developing embryo, a characteristic feature of double fertilization in angiosperms. The other options represent incorrect ploidy levels - 34 would be diploid, 68 tetraploid, and 17 haploid, none of which match the triploid nature of PEN.

The correct answer is (D) 51.