A chromosome unit (locus) is called an allele when it contains one of the viable DNA (deoxyribonucleic acid) coding units. The term ‘allele’ is usually used when referring to variations that code for a gene, but in some cases it is also used for variations that don’t code for a gene. The genotype of a gene is the set of alleles an individual has for that gene. When a creature is diploid, one which has two copies of each chromosome, each individual possesses two alleles, known as alleles. The gene for blossom color is a good example of this – a single gene determines the color of the petals, but there may be several different versions (or alleles) of it. It is possible for one version to result in red petals, while another one may An individual flower’s color depends on its two alleles for the gene and how they interact. An allele is an alternative form of a gene (in diploids, one of two) that is located at a specific position on a As an example, humans, like other diploid species, contain paired homologous chromosomes in their somatic cells and each gene is duplicated twice. In organisms in which both copies of a gene are identical – that is, they both possess the same allele – such a condition is known as homozygosity. When there are two alleles of a gene in the organism, it is said to be It is sometimes possible for an allele’s phenotypes (its traits) to be dominant or recessive, but most of the time At least one allele of its associated type must be present in order for a dominant phenotype to be exhibited, while alleles of its associated type must be present in order for a recessive phenotype to be exhibited.

It is true that heterozygotes express themselves differently in phenotype, but there are exceptions. A notable exception is incomplete dominance (sometimes referred to as blending inheritance), in which the traits of the allele blend This could be evident when crossing Antirrhinums – flowers with incompletely dominant “red” and “white” alleles for petal color – and finding that their offspring have There is also an exception to codominance when both alleles are present and both traits are expressed at the same time, such as both red and white petals springing from a single flower or flowers of two colors The dominance of blood types in humans is also obvious. If a person has one “A” blood type allele and one “B” blood type allele, their blood type would be It is also useful to note that wild type alleles are those that are considered “normal” for the organism, in contrast to mutant alleles, which are usually new modifications. The term ‘allele’ is now often used to describe variants in non-functional DNA, or junk DNA. With the advent of neutral genetic markers, it is now often used to describe a DNA sequence variation. In addition, there are multiple types of alleles, such as those that are seen in gene frequency tables for genetic markers, such as the DYS markers.