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Heterozygote | biology | Britannica

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biology Alternative Title: heterozygous allele

Learn about this topic in these articles:

autosomal dominant inheritance

  • In human genetic disease: Autosomal dominant inheritance

    It manifests itself in the heterozygote (designated Aa), who receives a mutant gene (designated a) from one parent and a normal (“wild-type”) gene (designated A) from the other. In such a case the pedigree (i.e., a pictorial representation of family history) is vertical—that is, the disease passes from one generation…

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combination of alleles

  • In allele

    …different, the organism’s genotype is heterozygous. A dominant allele will override the traits of a recessive allele in a heterozygous pairing. In some traits, however, alleles may be codominant—i.e., neither acts as dominant or recessive. An example is the human ABO blood group system; persons with type AB blood have…

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contrasted with homozygote

  • In homozygote

    In a heterozygous organism, or heterozygote, the genes for a specific trait are different.

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gene frequencies

  • In heredity: Population genetics

    …be more-complex proportions, including some heterozygotes. One possible intermediate stage is as follows: AA = 0.30, Aa = 0.20, aa = 0.50 The allele frequencies at such an intermediate stage can be calculated by “adding up” the alleles. Hence, the frequency of A will be 0.30 plus 1/2 of 0.20…

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  • In heredity: Selection

    …these alleles are sheltered in heterozygotes. Even though populations under selection technically are not in Hardy-Weinberg equilibrium, the proportions of the formula can be used as an approximation to show the relative proportions of homozygous recessives and heterozygotes. If a rare deleterious recessive allele is of frequency 1/50 in the…

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relationship to consanguinity

  • In consanguinity: Homozygosity and heterozygosity

    In genetics an allele that is carried at the same position in both of a pair of chromosomes is called homozygous. An allele may be rare in the general population, but, if the parent possesses it, it is transmitted from parent to child with…

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structure of genes

  • In evolution: Measuring gene variability

    …individuals in a population are heterozygotes at that locus. In a heterozygous individual the two genes for a trait, one received from the mother and the other from the father, are different. The proportion of heterozygotes in the population is, therefore, the same as the probability that two genes taken…

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  • In heredity: Discovery and rediscovery of Mendel’s laws

    …a hybrid plant, termed a heterozygote (Rr). Since the gene R, for purple, is dominant over r, for white, the F1 generation hybrids will show purple flowers. They are phenotypically purple, but their genotype contains both R and r genes, and these alternative (allelic or allelomorphic) genes do not blend…

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