Defining an Allele in Genetics
An allele is a specific version or variation of a gene. Just as a single word can have different spellings or pronunciations, a single gene can have different forms. Each of these forms is an allele. For most genes, an individual inherits two alleles, one from each biological parent.
Section 2: How Alleles Determine Traits
The combination of alleles an individual possesses for a particular gene is known as their genotype. This genotype is the genetic instruction that determines the observable physical or biochemical characteristic, called the phenotype. For example, the gene for pea plant flower color has an allele for purple flowers and an allele for white flowers.
Section 3: A Practical Example: Dominant and Recessive Alleles
Alleles can be dominant or recessive. A dominant allele expresses its trait even if only one copy is present, while a recessive allele's trait is only expressed if two copies are present. For instance, if the allele for brown eyes (B) is dominant over the allele for blue eyes (b), a person with the genotype Bb will have brown eyes because the 'B' allele masks the 'b' allele.
Section 4: Why Alleles are Important
The study of alleles is fundamental to understanding heredity and genetic variation within a population. This variation is the raw material for natural selection and evolution. Scientists also study alleles to understand the genetic basis of inherited diseases and traits.