In the context of biology, a allele turns out to be each of the alternative forms that a gene presents, which occupies the same position in each pair of homologous chromosomes, differs in its sequence and that can be manifested in specific modifications of the function of that gene.
The term allele has its origin in that of allelomorph, in the form of alleles, which is the same as saying that it is something that occurs in different ways within a population of individuals.
In the case of mammals, most of which turn out to be diploid (they have two series of chromosomes), they have two alleles of each gene, one that will come from the father and the other that will come from the mother. Each pair is located in the same place on the chromosome.
The allele must also be understood as the domain value that is attributed to a given gene when it competes with another gene for the occupation of the final position on the chromosomes, a situation that occurs during separation in cellular meiosis or cellular reproduction.
Then, the dominant value of the allele is that the transmission will become identical or different from the copy of the procreated gene.
Depending on the potency, an allele may be dominant in the situation and therefore express itself in the child with only one of the procreative copies, with which if the mother or father have it, the child will express it without doubt always. Or on the contrary, we may be facing the case of a recessive allele, for which two copies of the same gene will be needed, that is, two alleles for it to appear expressed on the procreated chromosome.
Among the types of alleles we find then the dominant allele and the recessive allele.
