What defines a dominant allele in genetics?

A dominant allele in genetics is one that expresses its trait even if only one copy is present in the genotype.

In more detail, genetics is the study of how traits are passed from parents to offspring. This is controlled by genes, which are segments of DNA that carry the instructions for making proteins, the building blocks of our bodies. Each gene has different versions, known as alleles. These alleles can be dominant or recessive.

A dominant allele is one that shows its effect on the phenotype, or physical appearance, of an organism, regardless of whether the individual has two copies of the allele (homozygous) or just one copy (heterozygous). This means that if an organism has at least one copy of a dominant allele, the trait that the allele codes for will be expressed.

For example, in humans, the allele for brown eyes (B) is dominant over the allele for blue eyes (b). So, a person with one brown-eye allele and one blue-eye allele (Bb) will have brown eyes because the brown-eye allele is dominant.

It's important to note that dominance does not mean that the allele is better, more powerful or more common. It simply refers to the way in which the allele's trait is expressed in the phenotype. Dominant alleles can code for traits that are advantageous, disadvantageous, or neutral in terms of survival and reproduction.

In summary, a dominant allele in genetics is one that expresses its trait in the phenotype, whether it is present in one copy (heterozygous) or two copies (homozygous). This is a fundamental concept in understanding how traits are inherited and expressed in living organisms.