Heterozygous

Heterozygous refers to the condition or state where an individual has two different forms of a particular gene, one inherited from each parent. The term is derived from the Greek words "heteros" meaning different and "zygon" meaning yoked or paired.

Definition

In genetics, a heterozygote is an individual having two different alleles of a particular gene or genes, and so giving rise to varying offspring. This variation can influence the phenotype of an organism, in which the two different alleles interact to produce a physical characteristic.

Heterozygous vs Homozygous

In contrast to a heterozygous organism, a homozygous organism has two copies of the same allele for a particular gene. The presence of identical alleles makes the organism homozygous for that gene. The phenotype of a homozygous organism will only display the traits associated with that particular allele.

Examples

An example of a heterozygous genotype is the Aa genotype for the seed shape in peas. The 'A' allele codes for round seeds, while the 'a' allele codes for wrinkled seeds. A plant with an Aa genotype will produce round seeds because the 'A' allele is dominant over the 'a' allele.

Importance in Medicine

In medicine, the concept of heterozygosity is important in understanding many genetic disorders. For example, in autosomal dominant disorders, an individual only needs one copy of the disease-causing allele to have the disorder. In contrast, in autosomal recessive disorders, an individual must be homozygous for the disease-causing allele to have the disorder.

See Also

• Genotype
• Phenotype
• Dominance
• Recessive
• Autosomal dominant
• Autosomal recessive

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