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.

    52/750 (page 48)
    48 GENERAL GENETICS Fig. 37. Ocular albinism. (Personal observation.) We cite as an example congenital nystagmus which generally is sex linked. In different families one finds a penetrance that varies from 0 to 3 to 73% (Hemmes, 1924) with all intermediate values (von Kibort, 1910, 25%; Cox, 1936, 36%; Semadeni, 1939, and Hanhart, 1953, 47%; Clarke, 1903, 50%; Guendet and Delia Porta, 1950, 53%; etc.). These facts show that dominance and recessiveness are not contradictory and explain how the same diseases can be transmitted in ways that appear to be different, i.e., sometimes as a dominant and sometimes as a recessive. Kerato- conus and pigmentary retinopathy are examples of such diseases. These facts are also useful in connection with genetic prognosis. This will vary according to the degree of penetrance prevailing within a family since penetrance does not usually vary within one and the same family. It becomes necessary, therefore, to seek and identify the heterozygotes in patients with incomplete penetrance. We shall return to this aspect in another chapter.