Alleles and inherited differencesSpec 3.12
Different forms of the same gene are called alleles. A gene for flower colour may have an allele for purple and an allele for white.
In body cells chromosomes are in pairs, so an organism usually has two alleles of each gene: one inherited from each parent. Individuals can have different combinations of alleles, so they have different inherited characteristics.
The alleles of a gene have slightly different base sequences, so they can code for slightly different versions of the same protein. This is why a difference in alleles can cause a difference in a characteristic.