In order to know the meaning of the term recessive allele, the first thing we have to do is proceed to discover the etymological origin of the two words that give it shape:
-Allelo is a neologism that was created in the 20th century and that comes from the Greek. Specifically, it derives from “allello” and means “two”.
-Recessive, on the other hand, is a word of Latin origin that is the fruit of the sum of three clearly delimited components: the prefix “re-”, which means “backwards”; “Cessus”, which can be translated as “walked” and the suffix “-ivo”, which is used to indicate active or passive relationship.
The notion of allele comes from allelomorph: that which can appear in different forms. In the field of biology, the value adopted by each gene that, in a pair, occupies the same space in the chromosomes that are homologous, is called an allele.
Recessive is an adjective that in biology is applied to hereditary characteristics that are not expressed in the phenotype of the one who has them, although they can manifest themselves in the descendants of the individual in question.
Understanding what a recessive allele is leads us to the notion of a dominant allele and, above all, to what is known as dominance. The alleles that make up the same gene are related to each other: dominance is the masking that one allele (the dominant allele) achieves from the expression of the phenotype of the other allele (the recessive allele).
The recessive allele, in this way, is the one whose expression of the phenotype is masked. It should be noted that being dominant or recessive is relative: in a gene with three alleles, for example, one allele can be recessive with respect to another and dominant over the third.
Recessive alleles are represented by lower case and dominant alleles by upper case.
To manifest, recessive alleles must appear alone. Suppose that the color yellow in a flower is a recessive allele. Thus, for the flower to determine its yellow color, it must have only the alleles that express that hue. In the case of dominant alleles, on the other hand, they are imposed by appearing in single or double doses and thus manage to express their characteristics.
When we talk about human beings, we have to explain that each gene is determined to have two alleles: one that comes from the father and another that comes from the mother. Based on this we find the fact that the allele that establishes that the son has brown eyes is dominant, however, the one with blue eyes is recessive.
This means that if the couple is made up of a father and a mother with brown eyes, their baby will have them brown. In the event that one of the two has them blue, it is most likely that the little one also has them brown due to the dominant allele, unless he inherits the recessive alleles from other relatives.