Inheritance

Offspring inherit features from their parents through genes. A gene is a section of DNA that codes for a characteristic, such as eye colour. You get two copies of each gene, one from each parent. Different versions of a gene are called alleles. A dominant allele (written with a capital letter, like B) shows its effect even if only one copy is present. A recessive allele (b) only shows if both copies are recessive.

In sexual reproduction, half the genes come from each parent, so offspring vary. A Punnett square shows the possible offspring of a cross. If two Bb parents have young, the possible combinations are BB, Bb, Bb and bb: three out of four show the dominant feature and one out of four shows the recessive one. In asexual reproduction there is only one parent, so offspring are genetically identical clones.