. Carnegie Institution of Washington publication. IN RATS AND GUINEA-PIGS. stripe of different extent, one group being of moderate size (12), the other extremely reduced (2). Twenty-eight individuals whose grades fell in the lower part of curve G (fig. 4), and averaged , were the parents of the next generation, group H. Individuals This generation consisted of 6 1 individuals having an aver- age grade of The varia- tion curve for this group (H, fig. 4), shows a nearly com- plete dropping out of individ- uals with the stripe of moder- ate size, such as occurred in group G. All the class
. Carnegie Institution of Washington publication. IN RATS AND GUINEA-PIGS. stripe of different extent, one group being of moderate size (12), the other extremely reduced (2). Twenty-eight individuals whose grades fell in the lower part of curve G (fig. 4), and averaged , were the parents of the next generation, group H. Individuals This generation consisted of 6 1 individuals having an aver- age grade of The varia- tion curve for this group (H, fig. 4), shows a nearly com- plete dropping out of individ- uals with the stripe of moder- ate size, such as occurred in group G. All the classes above 7 are small and the upward range stops at 22. A few individuals of lot H had no back-stripe at all (com- pare pi. i, fig. 3). These with some individuals having a much reduced stripe were se- lected as parents for the next generation, lot /. The aver- age grade of the parents was in this case ; that of their 34 young (lot 7, fig. 4) was 4. TwTenty-four of the 34 young fell in the lowest class, mean grade 2, while none were above class 12. The effect of selection in this series of experiments is clear from a comparison of the four curves, A, G, H, and /, fig. 4. vSelection has steadily lowered the average amount of pigmentation in theGr<?c/e race by reducing the Upward r . . range of the variation curve, thus eliminating the more abmodal variations, reducing the skewness of the curve, and diminishing the distance between mean and mode. One of the noteworthy features of the case is the absence of what may properly be. • — Effect of selection for back-stripe of reduced size in hooded rats, lots A, G, H, and 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 Carnegie Institution of Washington. Washington, Carnegie Institution of Washington
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