Allele

ABO blood type

Allele refers to one of two or more versions of a gene. An individual inherits two alleles for each gene, one from each parent. Alleles can result in different phenotypes or observable traits, depending on the way they interact with each other. The concept of alleles is fundamental to the understanding of genetics and plays a crucial role in the study of inheritance, genetic variation, and evolution.

Definition and Origin

The term "allele" originated from the Greek word allelon, meaning "of one another", which reflects the paired nature of alleles in diploid organisms. Alleles are specific sequences of DNA that code for a particular trait. While the genes are the same across all individuals of a species, alleles are the variations within those genes that lead to diversity in the population's physical appearance and physiological functions.

Types of Alleles

There are several types of alleles, including:

• Dominant alleles are those that express their trait even when only one copy is present. They are often represented by a capital letter (e.g., A).
• Recessive alleles only express their trait when two copies are present, one from each parent. They are usually denoted by a lowercase letter (e.g., a).
• Codominant alleles express both alleles simultaneously without blending, as seen in the AB blood type.
• Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the phenotypes of the homozygotes, such as in the case of pink flowers from red and white parents.

Allelic Variation

Allelic variation is the basis of genetic diversity within a population. It can occur through several mechanisms, including:

• Mutation, which is a change in the DNA sequence of a gene.
• Gene flow, which involves the transfer of alleles from one population to another.
• Genetic drift, which is a change in the allele frequency in a population due to random sampling of organisms.

Importance in Genetics

Alleles play a critical role in genetics, particularly in the study of genetic disorders and heredity. By understanding how alleles interact and express themselves, scientists can predict the likelihood of an organism inheriting certain traits, including diseases. This knowledge is crucial in fields such as genetic counseling, medicine, and biotechnology.

See Also

• Genotype
• Phenotype
• Homozygote
• Heterozygote
• Punnett square