Glossary

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Homozygous

Having two identical alleles of a gene

In the body cells of all higher animals and many plants, the chromosomes are always duplicated (diploid); in each case, one chromosome comes from the father and the other from the mother. Genes that are found on an identical (homologous) pair of chromosomes and are responsible for the same trait (e.g. flower colour) are called alleles. If the alleles on the two chromosomes are identical it means that the cell is homozygous in terms of this trait. The cell is heterozygous if the alleles are not identical (e.g. different expression of flower colour). In this case, the two alleles are different variants of a gene. One allele is usually dominant and determines the expression of the trait.