Allelic

Allelic

In genetics, the term allelic refers to anything related to alleles, which are different versions of a gene that exist at the same locus on homologous chromosomes. Alleles can vary in sequence and can lead to different traits or characteristics in an organism. The concept of alleles is fundamental to understanding genetic variation and inheritance patterns.

Definition

An allele is a variant form of a gene. Humans, for example, are diploid organisms, meaning they have two alleles at each genetic locus, with one allele inherited from each parent. The combination of alleles that an individual possesses is known as their genotype, and the observable traits that result from this genotype are referred to as the phenotype.

Allelic Variation

Allelic variation is the presence of different alleles at a gene locus. This variation is a key factor in the diversity of traits within a population. Allelic differences can arise through mutations, which are changes in the DNA sequence. These mutations can be as small as a single nucleotide change, known as a single nucleotide polymorphism (SNP), or as large as insertions or deletions of entire sections of DNA.

Dominance and Recessiveness

Alleles can exhibit different patterns of dominance. A dominant allele is one that expresses its trait even when only one copy is present, while a recessive allele requires two copies to express its trait. For example, in Mendelian inheritance, the allele for purple flower color in pea plants is dominant over the allele for white flower color.

Allelic Interactions

Allelic interactions can be complex, involving phenomena such as codominance, where both alleles in a heterozygote are fully expressed, and incomplete dominance, where the phenotype is a blend of the two alleles. Additionally, alleles can interact with other genes in epistasis, where the effect of one gene is modified by one or several other genes.

Allelic Frequency

The frequency of alleles in a population is a central concept in population genetics. Allelic frequency, or allele frequency, is the proportion of all copies of a gene in a population that are of a given allele type. Changes in allelic frequencies over time can indicate evolutionary processes such as natural selection, genetic drift, and gene flow.

Also see

• Gene
• Genotype
• Phenotype
• Mendelian inheritance
• Genetic variation
• Population genetics