Punnett’s matrix was the clearest. He called it a checkerboard, setting it up so that the female contribution was shown in the horizontal boxes and the male contribution in the vertical boxes. In each box, then, two gametes intersected—one from the top, one from the side—and it was an easy matter to write in the box which two gametes had paired to form each particular offspring. Punnett’s matrix first appeared in the third edition of his textbook, Mendelism, in 1911. Not until his death in 1967, at the age of ninety-one, was the checkerboard renamed the Punnett square. As a result, Punnett’s
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