Heterozygote

Heterozygote is a term used in genetics to describe an organism that has two different alleles of a gene. This is in contrast to a homozygote, which has two identical alleles of a gene. Heterozygotes can occur in both diploid organisms, where each cell contains two sets of chromosomes, and in haploid organisms, where each cell contains only one set of chromosomes.

Definition

A heterozygote is an individual organism that has two different forms (or alleles) of a given gene, one inherited from each parent. The term is derived from the Greek words "heteros" meaning different and "zygotos" meaning yoked or paired. In terms of genotype, a heterozygote is represented by two different letters (e.g., Aa or Bb).

Heterozygote Advantage

In some cases, being a heterozygote can confer an advantage over being a homozygote. This is known as heterozygote advantage or overdominance. An example of this is the sickle cell trait in humans. Individuals who are heterozygous for the sickle cell allele (i.e., they have one normal allele and one sickle cell allele) are resistant to malaria, whereas those who are homozygous for the normal allele or the sickle cell allele are not.

Heterozygote Disadvantage

Conversely, there can also be a disadvantage to being a heterozygote. This is known as heterozygote disadvantage or underdominance. An example of this is the cystic fibrosis trait in humans. Individuals who are heterozygous for the cystic fibrosis allele (i.e., they have one normal allele and one cystic fibrosis allele) are carriers of the disease, but do not exhibit symptoms themselves. However, they have a 50% chance of passing the disease allele on to their offspring.

See Also

• Genotype
• Phenotype
• Allele
• Homozygote
• Haploid
• Diploid
• Heterozygote advantage
• Heterozygote disadvantage

Heterozygote Resources
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