CBSE Class 10 Science 2019 · Paper 31/2/3 · Question 20

Sexual reproduction is the mode of reproduction in which two parents, a male and a female, produce gametes, and a male gamete fuses with a female gamete (fertilisation) to form a zygote, which develops into the new individual. More viable variation: the gametes are formed by meiosis and carry half the DNA, and at fertilisation the DNA of two different individuals is combined, so each offspring gets a new combination of characters, different from both parents. In asexual reproduction a single parent passes on copies of its own DNA, so the offspring differ only by rare DNA-copying errors and there is no mixing of characters. Since the combined variations come from healthy, living parents, they are viable. Effect on evolution: variations help some individuals survive changes in the environment; these individuals survive and reproduce more (natural selection), so useful variations accumulate over generations and can give rise to new species. By producing more variation, sexual reproduction promotes evolution.