Since most living beings are diploid, that is, they have two sets of chromosomes from the mother and the father, each gene also has a pair of alleles located at the same site on the chromosome. Consequently, the alleles can be dominant or recessive, the definition of each of them as well as their defining characteristics and the differences that exist between the two are presented in this article below.
The dominant alleles are those that determine the visible characteristics in the offspring, that is, they determine the phenotype. In addition to this, they determine the genotype, that is, the characteristics manifested at the genetic level inherited from one of the parents.
Each gene has two alleles, a recessive allele and a dominant allele, where the latter is manifested above the recessive allele. When both parents have dominant alleles, the offspring show new characteristics from the mix of alleles. This is due to the fact that, due to its dominance character, no allele can be superimposed on the other.
The dominant allele is expressed with the capital letter r (R) and when the two alleles are dominant they are expressed with RR.
Recessive alleles are those that are less likely to express or determine physical or genetic characteristics. These manifest only in the presence of another recessive allele. However, even if a recessive allele is not manifested in the phenotype or in the genotype of the offspring, it can still be present, since the one that is manifested is the dominant one, but the other pair is recessive.
When both parents have recessive alleles, the offspring show the characteristic of that gene. Recessive alleles are represented by the lowercase letter r (r), when both alleles are recessive they are represented by the symbol rr.
As seen in the previous definitions, alleles are the value assigned to a gene based on the dominance or recessiveness of the characteristic that determines said gene. The basic differences between dominant allele and recessive allele are summarized in the following table:
|dominant allele||recessive allele|
|The dominant alleles are those that determine the characteristic that is going to be expressed in the physical aspect or phenotype and in the genetic aspect or genotype.||Recessive alleles may be present but not manifest in the offspring, since they do not determine the presence of the characteristic.|
|Dominant alleles are represented by the capital letter erre (R).||Recessive alleles are represented by the lowercase letter r (r).|
|The dominant allele is manifested even in the presence of the recessive allele.||The recessive allele cannot manifest in the presence of the dominant allele.|
|Dominant alleles determine the visible characteristics of the offspring.||Recessive alleles only manifest if both parents pass it on to their offspring.|