Recessive allele

Recessive allele is a variant of a gene that does not express itself in the presence of a dominant allele. It is only expressed when two copies of the same allele are present in the organism's genetic makeup. This is known as homozygosity.

Definition

A recessive allele is one that is not expressed in the phenotype of a heterozygote. This means that if an organism has one copy of a dominant allele and one copy of a recessive allele (a condition known as heterozygosity), the trait associated with the dominant allele will be expressed. The trait associated with the recessive allele will only be expressed if the organism is homozygous for the recessive allele.

Examples

One of the most well-known examples of a recessive allele is the one that causes cystic fibrosis. This is a genetic disorder that affects the lungs and digestive system. An individual must inherit two copies of the recessive allele, one from each parent, in order to have the disease.

Another example is the allele for blue eyes. The allele for brown eyes is dominant, so an individual with one brown eye allele and one blue eye allele will have brown eyes. Only individuals with two blue eye alleles will have blue eyes.

See also

• Dominant allele
• Genotype
• Phenotype
• Homozygosity
• Heterozygosity

References

Recessive allele Resources
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