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    Author(s): Frank C. Sorensen
    Date: 1969
    Source: American Naturalist. 103: 389-398
    Publication Series: Scientific Journal (JRNL)
    PDF: Download Publication  (681 KB)


    Genetic load has been estimated for a number of outcrossing organisms, for example, Drosophila (Malogolowkin-Cohen et al. 1964), Tribolium (Levene et al. 1965), and man (Morton, Crow, and Muller 1956). However, little informaiton about load of deleterious genes in higher plants has been published. The purpose of this article is to provide some data on plants by reporting an estimate of embryonic load in coastal Douglas-fir as determined from comparison of set of sound seed following self-pollination and following controlled crossing with unrelated pollen.

    It was stated a decade ago (Dobzhansky 1957) that no estimates of frequency of deleterious and lethal genes were available for plants. This statement is still true in general, although some information does appear in the literature. For example, there are estimates or indications of load due to certain categories of genes in cultivated plants, especially genes causing chlorophyll deficiencies, as in maize (Crumpacker 1967) and pines (Eiche 1955; Snyder, Squillace, and Hamaker 1966). There are also data from some forest tree species, particularly coniferous species, which appear suitable for rough estimation of some part of the genetic load, although calculations of load have rarely been made (Fowler 1965b is an exception).

    The present data from coastal Douglas-fir were originally collected for purposes other than calculation of genetic load. However, the "control" appears good enough and the number of trees sampled large enough that a well-based estimate of load is possible. Because of this and because load estimates on plants are rare, the results from coastal Douglas-fir are presented in detail here.

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    Sorensen, Frank C. 1969. Embryonic genetic load in coastal Douglas-fir, Pseudotsuga menziesii var. menziesii. American Naturalist. 103: 389-398

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