16.3 Segregation: Mendel’s Key Discovery

Mendel’s most important discovery was that the F1 progeny of a cross between plants with different traits did not breed true. In the F2 generation, produced by allowing the F1 flowers to undergo self-fertilization, the recessive trait reappeared (Fig. 16.6). Not only did the recessive trait reappear, it reappeared in a definite numerical proportion. Among a large number of F2 progeny, Mendel found that the dominant:recessive ratio was very close to 3:1. The results he observed among the F2 progeny for each of the seven pairs of traits are given in Table 16.1. Across experiments for all seven traits, the ratio of dominant:recessive F2 offspring was 14,949:5010. Although there is variation from one experiment to the next, the overall ratio of 14,949:5010 equals 2.98:1, which is a very close approximation to 3:1.

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FIG. 16.6 Self-fertilization of the F1 hybrid, resulting in seeds of the F2 generation. The recessive trait appeared again in the F2 generation.
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