Question

Why is a Dominant allele called Dominant?

Answer 1

Genetics began or discovered by the work of Gregor Johann Mendel. Gregor Mendel published his work in $1866$ which was kept unrecognized till $1900$. He gave three theories- Law of Dominance- it states that recessive alleles will always express dominant phenotype. A gene has two versions-one is Dominant and other is recessive.

Complete answer:
Dominance is the phenomenon of one variant of a gene on a chromosome masking the effect of a different variant of the same gene on the other copy of the chromosome.
Dominant refers to that variant of the same gene. When reproduction or fertilization occurs the gene as alleles from each parent shows two versions one is dominance and recessive. If the alleles of a gene are to be different one allele will be expressed and that will be the dominant gene.
An allele which produces the same phenotype whether it's paired or not, identical or not they are called the dominant type. When an allele is dominant, they show variation in gene which produces a certain phenotype even if other allele-that is recessive is present. They just mask the effect of the other recessive allele. A dominant allele always suppresses the recessive allele. Alleles are nothing but functioning amino acids. The allele is dominant because one copy of the allele produces enough enzyme to supply a cell with sufficient product.

Note:
Combination is between two alleles of a gene. A dominant allele always results in showcasing its character over recessive allele. The alleles are homozygous if they code for one same trait and if they code for two different traits then heterozygous. So, two dominant alleles can survive if they exist in a homozygous pair and also the same two recessive alleles.