Heredity and sex . of hybrids there is a free separation of theelements derived from the two parents without regard towhich parent supplied them. An example will make this more obvious. Mendelcrossed an edible pea belonging to a race with yellowseeds to a pea belonging to a race with green seeds(Fig. 42). The offspring or first filial generation (Fi)had seeds all of which were yellow. When the plantsthat bore these seeds were self-fertilized, there wereobtained in the next generation, F2, both yellow andgreen peas in the proportion of 3 yellows to 1 green(Fig. 42). This is the well-known Mende
Heredity and sex . of hybrids there is a free separation of theelements derived from the two parents without regard towhich parent supplied them. An example will make this more obvious. Mendelcrossed an edible pea belonging to a race with yellowseeds to a pea belonging to a race with green seeds(Fig. 42). The offspring or first filial generation (Fi)had seeds all of which were yellow. When the plantsthat bore these seeds were self-fertilized, there wereobtained in the next generation, F2, both yellow andgreen peas in the proportion of 3 yellows to 1 green(Fig. 42). This is the well-known Mendelian ratioof 3:1. The clue to the meaning of this ratio was found whenthe plants of the second generation (F2) were green peas bred true; but the yellows were of two 76 HEREDITY AND SEX kinds — some produced yellow and green seeds againin the ratio of 3:1; others produced only yellowpeas. Now, if the yellows that bred true were counted,it was found that the number was but one-third ofall the Fig. 42. — Illustrating Moiid(>rH cross of yellow (lighter color) and green (dark color) peas. THE MENDELIAN PRINCIPLES OF HEREDITY 77 In other words, it was shown that the ratio of 3 yel-lows to 1 green was made up of 1 pure yellow, 2 hy-brid yellows, 1 pure green. This gave a clue to theprinciples that lay behind the observed results. Mendels chief claim to fame is found in the discoveryof a simple principle by means of which the entireseries of events could be explained. He pointed outthat if the original parent with yellow (Pi) carriedsomething in the germ that made the seed yellow, andthe original parent with green seeds (Pi) carried some-thing that made the seed green, the hybrid should con-tain both things. If both being present one domi-nates the other or gives color to the pea, all the peas inthe hybrid generation will be of one color — yellow inthis case. Mendel assumed that in the germ-cells ofthese hybrids the two factors that make yellow andgreen
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Keywords: ., boo, bookcentury1900, bookdecade1910, booksubjectsex, bookyear1913
