In the context of Biology, alleles are one of the alternative forms that present a gene occupying the same position in each pair of homologous chromosomes, being differentiated in its sequence and which can manifest itself in specific modifications of the function of this gene.
The term allele has its origin in the allelomorph and in the form of alleles, which is to say that something presents itself in different forms within a population of individuals.
In the case of mammals, most are diploid (they have two sets of chromosomes), they have two alleles of each gene, one of which will come from the father and the other from the mother. Each pair is located in the same place on the chromosome.
Alleles can 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 chromosomes, a situation that occurs during separation in cell meiosis or in cell reproduction
Then, from the dominant value of the alleles, identical or different transmission of the spawned gene copy will result.
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, thus, if the mother or father has it, the child will certainly express it as well.
Or, on the contrary, we may be faced with the case of a recessive allele, whereby two copies of the same gene, that is, two alleles, are needed to appear expressed on the procreated chromosome.
Thus, among the types of alleles, we find the dominant allele and the recessive allele.