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allele

An allele is one of the alternative forms or versions of a gene that can exist at a specific genetic locus (location) on a chromosome. Alleles are variations in the DNA sequence of a gene, and they can lead to differences in the traits or characteristics of an organism.

Key points about alleles include:

1. Gene Variants: Each gene in an organism's genome can have multiple alleles. These alleles may vary in terms of their DNA sequence, and they can lead to different forms of a particular trait. For example, there are different alleles for the gene that determines blood type in humans (A, B, O).

2. Homozygous and Heterozygous: An individual can have either two identical alleles at a specific genetic locus (homozygous) or two different alleles (heterozygous). For example, if an individual has two "A" alleles for a gene, they are homozygous for that gene. If they have one "A" and one "B" allele, they are heterozygous.

3. Dominant and Recessive: Some alleles are dominant, meaning that their trait is expressed when present in a heterozygous individual. Others are recessive, and their trait is only expressed when an individual is homozygous for that allele.

4. Phenotype: The combination of alleles an individual has at a specific gene locus determines their phenotype, which is the observable physical or functional expression of the trait associated with that gene.

5. Mendelian Genetics: Alleles play a central role in Mendelian genetics, which describes how traits are inherited from one generation to the next. The genotype of an individual, which represents their allele combinations, determines their potential phenotypes and the traits they can pass on to their offspring.

6. Multiple Alleles: Some genes have more than two alleles at a given locus. For example, the human HLA system, which is involved in immune responses, has many different alleles.

Alleles are fundamental to understanding inheritance, genetic diversity, and the variations in traits observed in populations. They are at the heart of genetics and heredity, and their interactions determine the genetic makeup and characteristics of individuals.

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