Question

The ratio of chromosomal number of pollen grain of Nicotiana tabacum; endosperm cell of Oryza sativa and root cell of Allium cepa is

• A. 6 : 9 : 4
• B. 3 : 8 : 2
• C. 3 : 9 : 2
• D. 4 : 7 : 6

Answer 1

The correct option is A 6 : 9 : 4

Pollen grain is the first cell of immature male gametophyte and is produced by meiosis in diploid microspore mother cells (2n); this makes it a haploid structure. Since the diploid chromosome number in Nicotiana tabacum is 2n=48; its pollen grain has n=24 chromosomes. Primary endosperm nucleus is the product of triple fusion wherein the haploid male gamete fuses with diploid secondary nucleus/central cell and forms triploid endosperm (3n). Since the haploid chromosome number for Oryza sativa is n= 12; its primary endosperm nucleus (3n) will have 36 chromosomes. Root cells are the diploid cells which carry the same chromosome number as is found in other somatic cells of that species. Since the diploid chromosome number (2n) for Allium is 16; its leaf cells (2n) will have 16 chromosomes. This makes the ratio of chromosome number in pollen of Nicotiana tabacum (24), endosperm cell of Oryza sativa (36) and root cells of Allium (16) is 6: 9:4. Option A is the correct answer.