Question

The male gametes are x and the egg is 3x. The ploidy level in embryo and endosperm will be
(a) 4x in the embryo and 4x in the endosperm
(b) 4x in the embryo and 7x in the endosperm
(c) 4x in the embryo and 6x in the endosperm
(d) 6x in the embryo and 12x in the endosperm

Answer 1

Hint: Gametes are haploid (n). An embryo is formed as a result of the fertilization of gametes whereas Endosperm is a result of triple fusion.

Complete answer:
Both male and female gametes are haploid. In this case, the male gamete (n) has a haploid number of x. The female gamete(N) has a haploid number of 3x.
Since the embryo is formed as a result of the fusion of gametes, The ploidy level of the embryo is diploid (N+ n) .
So, in this case, the ploidy level of the embryo is 3x+x which is 4x.
The endosperm is a result of double fertilization or triple fusion. In 70% of the angiosperms, Endosperm is polyploid as it is formed as a result of the fusion of one male gamete with the central cell of the gametophyte.
The central cell of the gametophyte is diploid (2N) . So, in this case, the ploidy of the Central cell is 2(3x) which is 6x.
Since Endosperm is formed by the fusion of male gamete with the central cell Its ploidy is triploid (2N+n) So, in this case, the ploidy level of Endosperm (2N + n) is 6x + x which is 7x.
So, the answer is ‘4x in the embryo and 7x in endosperm’.

Note: The endosperm is polyploid in 70% of Angiosperms and can vary from 2n to 15n. But in most cases, it is triploid. Endosperm replaces the female gametophyte to take its place as the nutritive tissue for the embryo.