CBSE Class 10 Science 2017 · Paper 31(B)/C · Question 12

Four main steps, in sequence: 1. Formation of gametes: the male and female parents form gametes, each with half the number of chromosomes of the body cells. 2. Fertilisation: a male gamete and a female gamete fuse. 3. Formation of the zygote: the fused cell, the zygote, has the full number of chromosomes again (in humans, $23+23=46$). 4. Development of the embryo: the zygote divides repeatedly to form an embryo, which develops into a new individual. Two advantages of sexual reproduction: First, it produces more variation in the offspring, because the DNA of two parents is combined in new ways. Second, this variation helps the species to survive changes in its environment, and it is the basis of evolution.