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What Are Alleles?

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Alleles

Alleles determine traits like seed color and pod color.

Credit: Steve Berg
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An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. These DNA codings determine distinct traits that can be passed on from parents to offspring. The process by which alleles are transmitted was discovered by Gregor Mendel and formulated in what is known as Mendel's law of segregation.

Mendel studied various characteristics of pea plants, one of which was seed color. The gene for seed color in pea plants exists in two forms. There is one form or allele for yellow seed color (Y) and another for green seed color (y). One allele is dominant and the other is recessive. In this example, the allele for yellow seed color is dominant and the allele for green seed color is recessive. Since organisms have two alleles for each trait, when the alleles of a pair are heterozygous, the dominant allele trait is expressed and the recessive allele trait is masked. Seeds with the genetic makeup of (YY) or (Yy) are yellow, while seeds that are (yy) are green.

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