heterozygoot

A heterozygote is an organism that carries two different alleles at a specific genetic locus, one on each chromosome of a homologous pair. For example, a genotype described as Aa consists of allele A inherited from one parent and allele a from the other. This is in contrast to a homozygous genotype, such as AA or aa, where both alleles are the same.

In many genes, one allele is dominant over the other, so the phenotype of a heterozygote Aa often resembles that produced by the dominant allele. However, dominance is not universal; some genes show incomplete dominance, where neither allele completely masks the other, or codominance, where both alleles contribute to the phenotype.

Medical and biological contexts often consider heterozygotes in relation to recessive diseases. If the disease-causing allele is recessive, individuals with a heterozygous Aa genotype are typically carriers who do not show disease symptoms but can pass the allele to offspring. If two carriers mate, there is a chance of producing affected offspring (typically 25% for a recessive trait, depending on the specific allele) when the other parent contributes the recessive allele.

Heterozygote advantage refers to situations where being heterozygous increases fitness compared to both homozygous forms, such as certain heterozygous combinations that confer resistance to particular diseases. In population genetics, heterozygosity is a measure of genetic diversity, reflecting how many individuals carry two different alleles at a locus.