Heredity in ophthalmology / Jules François.

  • François, J. (Jules)
Date:
1961
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Heredity in ophthalmology / Jules François. Source: Wellcome Collection.

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    DOMINANT AUTOSOMAL INHERITANCE 23 Affected homozygote Healthy homozygote Parents Gametes Children Affected heterozygotes (100%) Fig. 7. Dominant autosomal heredity. Crossing of an affected homozygote and a normal homozygote. Affected homozygote Affected heterozygote Porents Gametes Children Affected homozygotes (50%) Affected heterozygotes (50%) Fig. 8. Dominant autosomal heredity. Crossing of an affected homozygote with an affected heterozygote. homozygotes (AA) and 50% defective heterozygotes (Aa), both exhibiting the same phenotype. The third possibility is the union of two defective homozygotes (Fig. 9). Each of these produces only gametes bearing the pathologic gene (A), and the result will be that all offspring are defective homozygotes. One can ask whether the diseased homozygote and the diseased heterozygote have the same phenotype. It is quite difficult to answer this question since identical phenomena are rare in human genetics. It appears, however, that one can consider three possibilities. (1) There is no phenotypic difference between a homozygote and a heterozygote, as for example in a family with congenital cataracts described in 1934 by Komai (Fig. 10). (2) The homozygote might show a more intense defect than the heterozygote, as occurred in a family (François,