Heterozygous
Say it: het-uh-roh-ZY-gus
Heterozygous describes an organism that carries two different alleles of a gene at a given locus, such as one dominant and one recessive allele.
Also: heterozygote, heterozygosity
Definition
What does heterozygous mean?
An organism is heterozygous for a gene when the two alleles at that locus, one inherited from each parent, are different. A plant with the genotype Aa is heterozygous, while plants that are AA or aa are homozygous. Like homozygous, the term always refers to a particular locus, so an individual can be heterozygous for some genes and homozygous for others.
What a heterozygote looks like depends on how its two alleles interact. With complete dominance it shows the dominant trait and carries the recessive allele hidden, so a person heterozygous for a recessive disease allele is usually an unaffected carrier. With incomplete dominance it is intermediate, like pink snapdragons from red and white parents, and with codominance both alleles show, as in people with blood type AB or MN. Heterozygotes make two kinds of gametes in equal numbers, so crossing two of them gives the classic 1:2:1 ratio of genotypes.
The share of heterozygous loci is a common measure of genetic diversity in a population, and Hardy–Weinberg equilibrium predicts the frequency of heterozygotes for a two-allele gene as 2pq.
Word parts
Where does the word “heterozygous” come from?
- hetero-
- other, differentGreek heteros
- zyg-
- yoke, joined pairGreek zygon
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Terms that go with it
- HomozygousHomozygous describes an organism that carries two identical alleles of a gene at a given locus, one inherited from each parent.
- AlleleAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
- GenotypeA genotype is the genetic makeup of an organism, either at one locus, such as Aa, or across its whole genome, including alleles it does not express.
- Dominant alleleA dominant allele is a version of a gene whose effect shows in the phenotype even when only one copy is present, masking a recessive allele.
- Recessive alleleA recessive allele is a version of a gene whose effect appears only when an organism has two copies, because a single dominant allele masks it.
- Hardy–Weinberg equilibriumHardy–Weinberg equilibrium is the state in which allele and genotype frequencies in a population stay constant from one generation to the next.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Heterozygous
- OpenStax Biology 2e, 12.2 Characteristics and Traits
- MedlinePlus Genetics: What are the different ways a genetic condition can be inherited?
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