Heterozygote

Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. When an organism is referred to as a heterozygote or as being heterozygous for a specific gene, it means that the organism carries a different version of that gene on each of the two corresponding chromosomes. Heterozygosity refers to the state of being a heterozygote, but in population genetics, it commonly refers to the fraction of individuals in a population that are heterozygous for that locus.

Related Topics:
Diploid - Polyploid - Alleles - Locus - Chromosomes - Gene - Population genetics

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In a heterozygous individual, each allele produces its own unique protein or enzyme. The result is a mixture of the two rather than a combination of the two into one. If the presence of the abnormal enzyme produces an abnormal effect in the heterozygote, the abnormal allele is termed a dominant gene. In other cases, especially when the abnormal allele produces a nonfunctional enzyme, the abnormal enzyme molecules have no obvious effect on the heterozygote. The individual is an asymptomatic carrier of the abnormal allele, which is referred to as a recessive gene.

Related Topics:
Dominant - Asymptomatic carrier - Recessive

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To symbolize how a gene is inherited (Main article: Mendelian inheritance), the dominant allele is indicated with an upper case character and the recessive with a lower case character. The colour of Mendel's peas are often indicated as PP for the dominant homozygote, which produces a pink flower, and pp for the recessive homozygote, which produces a white flower. When these are crossed, the F1 or first filial generation receives a chromosome with the P gene from the pink-flowered parent and a corresponding chromosome with the p gene from the white-flowered parent. All of the F1 generation are heterozygous, and this is indicated with Pp. All of the F1 plants produce pink flowers.

Related Topics:
Mendelian inheritance - Dominant

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Some genes are neither dominant nor recessive to another allele. In such cases, both genes affect the heterozygote. Sometimes the result is intermediary: when a red carnation is crossed with a white carnation, they produce heterozygous carnations with pink flowers. If the test is sensitive enough, the heterozygote has the phenotype of both parents: when a person who is homozygous for the A blood type gene marries a person who is homozygous for the B blood type gene, they produce heterozygous children who test positive for both A and B blood type.

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