An organization is hétérozygote for a gene when it has two Allèle S different from this gene on same a Locus for each one of its homologous Chromosomes.

Such an organization must be at least Diploïde (two homologous chromosomes in each cell), or Polyploïde (more than two homologous chromosomes in each cell). In the organizations diploïdes, the two various alleles are inherited the Gamète S of both relative S. These various alleles contain different codes Génétique S.

An allele can take precedence over another (it is said whereas it is dominating) but two alleles can be also expressed simultaneously in the same feature (alleles neither dominant nor recessive). In such cases, the two alleles influence the phenotype of the hétérozygote. For example, a plant with red flowers crossed with a plant with white flowers will give a plant to pink flowers.

In other cases, the phenotype of the hétérozygote " exprime" two alleles. For example, when an individual Homozygote carrying a standard blood of has fertilizes an individual carrying a blood of the type B, they give rise to a descent generating of the antibodies has and B (one speaks then about " Co-dominance").

Use of the term

The carrying term “hétérozygote” is used as much in Physiologie as in Pathologie.

In physiology

• the Phénotype rhesus of the blood groups is either positive or negative. The positive allele being dominating compared to the negative allele, the phenotype Groupe positive Rhesus corresponds to two positive alleles, that is to say with a positive allele and a negative allele. In the event of pregnancy at a woman Rh negative with a procreator Rh positive, the determination of the character homozygote or hétérozygote of the procreator makes it possible to calculate the probability of having a child Rh positive.

In pathology

• In the event of disease with dominant Transmission autosomic, the sick person is Homozygote (what is very rare) that is to say hétérozygote.

• In the event of disease with recessive autosomic Transmission, the sick person is always homozygote. If both loci have each one a different allele transferring, one speaks about “hétérozygote composite”. The people suffering from a disease with recessive autosomic Transmission have obligatory parents “hétérozygotes”.

• In the event of recessive Transmission related to X, the women are very often hétérozygotes and do not express the disease, while the men are (inevitably!) hétérozygotes and always expresses the disease. A woman can be “hétérozygote symptomatic” because of the nonrandom Inactivation of the X chromosome.

• the composite double hétérozygotie or hétérozygotie: presence of two transferred different alleles, one coming from the mother, the other coming from the frequent father in the case of the mucoviscidose for example.

See too

• Polymorphism

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