Alleles

Alleles are different forms of a gene that arise by mutation and are found at the same place on a chromosome. In a diploid organism, each individual inherits two alleles for each gene, one from each parent. These alleles can be the same or different, leading to homozygous or heterozygous conditions, respectively.

Types of Alleles

Alleles can be classified into several types based on their effects on the phenotype:

• Dominant - An allele that expresses its phenotype even in the presence of a different allele.
• Recessive - An allele that only expresses its phenotype when paired with an identical allele.
• Codominant - Both alleles in a heterozygous individual contribute to the phenotype.
• Incomplete Dominance - The phenotype is a blend of both alleles in a heterozygous individual.

Function and Importance

Alleles play a crucial role in genetic variation and evolution. They are responsible for the diversity of traits within a population. The combination of different alleles can lead to variations in traits such as eye color, blood type, and susceptibility to certain diseases.

Mendelian Inheritance

The concept of alleles is fundamental to Mendelian inheritance, which describes how traits are passed from parents to offspring through discrete units of inheritance. Gregor Mendel's experiments with pea plants laid the foundation for understanding how alleles segregate and assort independently during meiosis.

Genetic Disorders

Certain genetic disorders are caused by mutations in alleles. For example:

• Cystic fibrosis is caused by a recessive allele.
• Huntington's disease is caused by a dominant allele.

Research and Applications

Understanding alleles is essential in fields such as genetics, medicine, and agriculture. Techniques like genetic engineering and gene therapy rely on manipulating alleles to achieve desired outcomes.

See Also

• Gene
• Chromosome
• Genotype
• Phenotype
• Mutation
• Genetic variation
• Evolution