(allelomorph) A form in which a gene may occur. Different alleles of a gene give rise to different expressions of a character. Hence alleles for 'green' and 'yellow' are alternative expressions of the gene governing the characteristic for seed colour. Alleles of a gene always occupy the same site (locus) on homologous chromosomes. A diploid organism whose cells contain two identical alleles is said to be * homozygous . One with two different alleles at a locus is said to be * heterozygous . The allele expressed in a heterozygous organism depends on the dominance relationship between the two alleles. If one is expressed to the exclusion of the other it is described as * dominant and the latter * recessive . If the heterozygote is intermediate in appearance between the two homozygotes, the alleles are said to exhibit * incomplete dominance. |
