When we inherit a trait - for example, hair colour – from a parent, it is not the gene, strictly speaking, that is inherited. Instead, it is what is called an allele. This is a gene variation. The genetic pioneer, Gregor Mendel, theorised about alleles by observing the colours of flowers. He supposed that male plants could offer one of two alleles and the same occurred with females. Depending on the colour of the flower of both parents, so the colour of the flower of the offspring plant could be determined. Humans have the same diploid form of genetic inheritance that relies on these pairs of alleles.