In sexual reproduction the new-born gets half its genes from each parent, so it resembles both parents in some characters but is not identical to either.
Gametes are formed by meiosis, so each sperm and ovum carries only one set (haploid) of chromosomes. At fertilization they fuse and the zygote gets a full set: one from the father and one from the mother. The genes of the two parents are recombined in the child.
Examples:
- A child may have the eye colour or curly hair of the mother and the height or skin colour of the father.
- Brothers and sisters of the same parents look alike in many features, yet each looks different, because each receives a different combination of parental genes. (Only monozygotic twins, formed from one zygote, are exactly similar.)
- In plants, seeds produced by cross-pollination grow into plants that show some characters of both parent plants; this is used to develop new high-yielding varieties.
This genetic variation helps organisms adjust to changing environments and is the basis of evolution.