How do alleles contribute to genetic variation?

Alleles contribute to genetic variation by providing different versions of genes that code for various traits.

Alleles are different forms of the same gene, each carrying a unique sequence of DNA. They are located at the same position, or locus, on a chromosome. Each individual inherits two alleles for each gene, one from each parent. These alleles may be identical (homozygous) or different (heterozygous), and it's this combination that contributes to genetic variation.

When an organism reproduces, its alleles are passed on to its offspring. In sexual reproduction, the offspring receives a mix of alleles from both parents. This process, known as recombination, results in a unique combination of alleles in the offspring, contributing to genetic variation.

Furthermore, mutations can also create new alleles. A mutation is a change in the DNA sequence of a gene. While many mutations are harmful or neutral, some can be beneficial and increase an organism's chances of survival. These beneficial mutations can then be passed on to future generations, further contributing to genetic variation.

In addition, the environment can influence how genes are expressed, leading to variation. For example, identical twins have the same alleles, but environmental factors such as diet and lifestyle can cause differences in their physical appearance and health.

In conclusion, alleles contribute to genetic variation by providing different versions of genes, through recombination during sexual reproduction, through mutations, and through environmental influences on gene expression. This genetic variation is crucial for the survival and evolution of species, as it enables populations to adapt to changing environments.