What is the difference between dominant and recessive alleles?

Dominant alleles express their traits even if only one copy is present, while recessive alleles require two copies to express their traits.

In genetics, alleles are different forms of the same gene. Each individual inherits two alleles for each gene, one from each parent. These alleles can either be dominant or recessive. Dominant alleles are those that express their traits or characteristics even if only one copy is present in the pair. This means that if an individual inherits a dominant allele from either parent, the trait associated with that allele will be expressed.

On the other hand, recessive alleles are those that require two copies to express their traits. This means that the trait associated with a recessive allele will only be expressed if the individual inherits the same recessive allele from both parents. If an individual inherits a dominant allele and a recessive allele, the dominant trait will be expressed, and the individual will be a carrier of the recessive trait.

This principle of dominant and recessive alleles is a fundamental concept in Mendelian genetics, named after Gregor Mendel, the father of modern genetics. Mendel's experiments with pea plants in the mid-19th century led to the discovery of these principles. He observed that certain traits, such as flower colour and seed shape, would appear in offspring even if they were not present in the parents, leading to the concept of dominant and recessive traits.

In terms of notation, dominant alleles are typically represented by uppercase letters, while recessive alleles are represented by lowercase letters. For example, if 'A' represents a dominant allele and 'a' represents a recessive allele, an individual with 'AA' or 'Aa' will express the dominant trait, while only an individual with 'aa' will express the recessive trait.

It's important to note that being dominant does not mean an allele is better, more powerful or more common. It simply refers to the way in which the allele's trait is expressed. Both dominant and recessive alleles play crucial roles in genetic diversity and evolution.