. The elements of genetics. Genetics. 100 ^ fi 80 CO 40 ^ 20 WO 80 60. *» IV X t930 IV X If X 1933 /V X /93^ IV X /S35 Fig. 74.—The percentages of the population of the ladybird Adalia punctata with black and red ground colours in April (IV) and October (X) over a period of six years in Buch, Germany. There is a regular seasonal change in the frequencies of these genetically controlled alternatives, red being commoner in spring than it is in autumn (after TimofeefF-Ressovsky, 1940). relative frequencies of allelomorphs of genes or super-genes govern- ing polymorphism in an ephemeral (Fig. 74);
. The elements of genetics. Genetics. 100 ^ fi 80 CO 40 ^ 20 WO 80 60. *» IV X t930 IV X If X 1933 /V X /93^ IV X /S35 Fig. 74.—The percentages of the population of the ladybird Adalia punctata with black and red ground colours in April (IV) and October (X) over a period of six years in Buch, Germany. There is a regular seasonal change in the frequencies of these genetically controlled alternatives, red being commoner in spring than it is in autumn (after TimofeefF-Ressovsky, 1940). relative frequencies of allelomorphs of genes or super-genes govern- ing polymorphism in an ephemeral (Fig. 74); but this is a special case. Permanent adaptation must generally demand the irreversible fixation of genes, and if this can be brought about by permanent changes, so it can by temporary ones too. In responding thus to non-permanent changes, the stock will gain nothing in fitness, and will lose some of the variability on which prospective adaptation must depend, by the profitless fixation of free variation under the erratic selection. This loss must be made good in the long run by new variability from mutation (Fig. 71), as indeed must any reduction in variability whatever its cause, if the species is to survive. In fact the amount of variability, when at equihbrium in a popula- tion, will be such that the loss, itself proportional to the free and 295. 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 Darlington, C. D. (Cyril Dean), 1903-; Mather, Kenneth. New York : Macmillan
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Keywords: ., bookcentury1900, bookpublishernewyorkmacmil, booksubjectgenetics
