Some people are right handed. Others are left handed.
Some people are blonde. Others are dark haired.
Some people can roll their tongue. Others cannot.
What makes these people appear the way they do? The answer is genes. Genes are parts of chromosomes, and they control the characteristics which are passed on from parents to children. When an egg is fertilised, genes from the father and the mother combine to form a new person. Each set of genes contains half the information needed to make a new human.
