. Biology and human life. Biology. 2D: 2R. Fig. 214. Mendel's law of segregation When two individuals with a pair of alternative characters are mated, the offspring will all have the character of one of the parents; this char- acter is called the dominant one, and the alterna- tive character is called the recessive. The hybrid offspring of such a mating is represented in the diagram by F-^. Offspring of this kind resemble the dominant parent, D, but experiments show that there is a real difference. If such a hybrid is mated with one of the pure dominant type, /, the next generation will all ap
. Biology and human life. Biology. 2D: 2R. Fig. 214. Mendel's law of segregation When two individuals with a pair of alternative characters are mated, the offspring will all have the character of one of the parents; this char- acter is called the dominant one, and the alterna- tive character is called the recessive. The hybrid offspring of such a mating is represented in the diagram by F-^. Offspring of this kind resemble the dominant parent, D, but experiments show that there is a real difference. If such a hybrid is mated with one of the pure dominant type, /, the next generation will all appear dominant. If such a hybrid is mated with an individual of the recessive type, 2, the offspring will consist of dominants and recessives, in about equal num- bers. If two such hybrids are mated, 3, the off- spring will show both dominants and recessives, in the proportion of three to one. This splitting up of the offspring of hybrids into two types showing ancestral factors is almost universal; it is called segregation with green seeds (see table on opposite page) ; that is, the two original parental types reappear. There is segregation in the proportion of three dominants to one reces- sive (3:1). By inbreed- ing a second time we find further segregation (col- umn marked "Third Hy- brid Generation"). But here a new fact appears: some of these plants in the second hybrid gen- eration breed true—some of the yellows (dom- inant) and all of the greens (recessive). The greens are found to breed true in every succeeding generation, in spite of the fact that they were derived from yellow hy- brids. Plants (or ani- mals) that behave in this manner are called extracted recessives. Re- gardless of the fact that they have descended from yellow (dominant) plants (first hybrid gen- eration), such recessives are considered pure be- cause they always do breed true. Again, those. Please note that these images are extracted from scanned page images that may have been digitally
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