WAEC Biology 2011 Papers

Concept:In flowering plants, the endosperm is a triploid tissue ($3n$), while the hybrid plant body is diploid ($2n$).Explanation:The endosperm develops from the fusion of one male gamete with two polar nuclei.So, its chromosome number is always three times the gametic number ($n$).Given that the endosperm cell has $36$ chromosomes:$$3n = 36 \Rightarrow n = 12$$This shows that each gamete from either parent variety contains $12$ chromosomes.When two varieties are crossed, their gametes fuse to form the hybrid.The hybrid receives one complete set of chromosomes from each parent.Hence, the hybrid's chromosome number becomes diploid:$$2n = 2 \times 12 = 24$$Answer:B. 24