. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 540 GENETICS IN RELATION TO AGRICULTURE equality of males and females in every generation. Extensive statistical in- vestigations of the sex-ratio in a number of animals demonstrate, however, that there are usually small but significant deviations from the numerical equality of the sexes. The data in Table LXX collected by Morgan illustrate this point. In man the sex-ratio varies among different peoples, but almost in- variably the proportion of males is slightly in excess of that of
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 540 GENETICS IN RELATION TO AGRICULTURE equality of males and females in every generation. Extensive statistical in- vestigations of the sex-ratio in a number of animals demonstrate, however, that there are usually small but significant deviations from the numerical equality of the sexes. The data in Table LXX collected by Morgan illustrate this point. In man the sex-ratio varies among different peoples, but almost in- variably the proportion of males is slightly in excess of that of Fig. 213.—Frequency polygon of head lengths of spermatozoa in the pig. (Data from Wodsedalek.) In dealing with sex-ratios it must be emphasized that a study of the deviations which are obtained may point to conditions which alter the sex-ratio without disturbing the mode of determination of sex. The mechanism of sex-determination is not such a one as would lead invari- ably to numerical equality of the sexes. This may easily be seen by a consideration of several disturbing factors which may enter into it. The first of these has to do with the relative sizes of male and female producing gametes, particularly in those animals in which the male is the heterozygous sex. Thus AVodsedalek has shown for the pig and the horse that there are two intergrading classes of spermatozoa as respects size (Figs. 213 and 214). Unquestionably in both cases the larger class Digitized by Microsoft®. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Babcock, E. B. (Ernest Brown), b. 1877; Clausen, Roy Elwood, 1891-. New York, McGraw-Hill; [etc. , etc. ]
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