Heterocigotos

Heterocigotos are organisms that carry two different alleles at a single gene locus in a diploid genome. The state is called heterozygosity and it contrasts with homozygosity, where both alleles are the same. In sexually reproducing species, offspring inherit one allele from each parent, resulting in heterocigotos when the two copies differ.

The phenotype of a heterocigoto depends on the dominance relationship between the alleles. In complete dominance, the phenotype matches the dominant allele and the recessive allele has no visible effect. In incomplete dominance, the phenotype is intermediate between the two alleles. In codominance, both alleles contribute to the phenotype. A classic example of codominance is the ABO blood group system, where IA and IB are codominant and i is recessive; IAIB individuals express the AB blood type, IAi express A, and IBi express B. Heterocigotos for other traits can display normal or altered phenotypes depending on the specific gene and alleles, such as the HbA HbS combination (sickle cell trait), which usually causes no severe symptoms but can confer some malaria resistance in certain populations.

Significance and applications: Heterocigotos contribute to genetic variation within populations and can influence fitness. Heterozygous advantage can maintain deleterious alleles in a population, a concept in evolution. In population genetics, heterozygosity is used to measure genetic diversity (for example, 2pq under Hardy-Weinberg equilibrium). In medicine and breeding, identifying heterocigotos is important for predicting inheritance patterns, carrier status, and potential trait expression.