CBSE Class 10 Science 2017 · Paper 31/1/3 · Question 14

Four steps in sexual reproduction: (1) Formation of gametes: male and female gametes are formed in the reproductive organs, each with half the number of chromosomes of a body cell. (2) Transfer of gametes: the male gamete is brought to the female gamete (pollination in flowering plants; transfer of sperms into the female body in humans). (3) Fertilisation: the male and female gametes fuse to form a zygote, which has the full number of chromosomes. (4) Development: the zygote divides repeatedly to form an embryo, which grows into a new individual. Two advantages: (i) The offspring get DNA from two parents, so sexual reproduction produces more variation than asexual reproduction. (ii) Variation helps a species survive when conditions change and, accumulated over generations, is the basis of evolution.