[单项选择]Ever since Gregor Mendel’s famous experiments with hybrid sweet peas, it has been known that there must be unitary elements within the cells which exert control over inherited characteiristics, and for a long time there was considerable speculation about what these were. These elements came to be known as genes, and although they were long treated as hypothetical constructs, a great deal of knowledge about them slowly accumulated. It came to be known, for example, that each gene had to be passed along virtually unchanged from generation to generation; that there must be many thousands of these particles in every human cell, distributed unevenly among the twenty-three pairs of chromosomes; that each gene must occupy a very definite place (locus) on its chromosome; and that each pair of homologous chromosomes had to contain homologous assortments of genes, arranged with few exceptions in precisely the same order on each member of the chromosome pairs. A wonderfully complex and fruitful s
A. Twenty-two.
B. Twenty-three.
C. Twenty-six.
D. Forty-six.

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