Fluctuations of Sampling in a Mendelian Population.
نویسنده
چکیده
In experimental crosses with pedigreed cultures, the observed Mendelian ratios are supposed to be due to the chance combinations of 2” kinds of gametes (n = number of allelomorphic pairs) occurring in equal numbers. The total or aggregate results may show larger or smaller deviations from the calculated ratios, but these deviations frequently lie within reasonable limits of error on the hypothesis of simple sampling. The aggregate results are obtained by adding subgroups-litters, families, pods, cobs, plants, or the like, in the experiments. The subgroups themselves may show extreme deviations. The theory of simple sampling which underlies strict Mendelism does not preclude such fluctuation in subgroups but calls for fluctuations of various sizes with expected frequencies. One could hardly postulate Mendelian inheritance with few or no deviations in subgroups or in totals. However, it is entirely conceivable that the total results in a Mendelian experiment may agree closely with the calculated ratio, and yet pure chance may not be operative, for extreme plus and minus deviations in the subgroups may counterbalance each other. YULE (1914) drew attention to such a case in analyzing LOCK’S data on maize, for although the means agree very well with expection, “the contrast between DR’s selfed and the DR X RR crosses is curious. The former certainly do not suggest any significant fluctuation; the latter do on the whole suggest some source of disturbance or possibly error.” Mendel recognized wide fluctuations in the subgroups, and recorded in his original paper four plants which gave dominants to recessives in the ratios of 43 : 2, 32 : I , 14 : 15, and 20 : 19. While such departures are not utterly impossible, their occurrence should be extremely infrequent. The odds against a ratio of 20:19, for example, are about
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ورودعنوان ژورنال:
- Genetics
دوره 3 6 شماره
صفحات -
تاریخ انتشار 2003