H. Morgan and his associates have worked out an
ingenious method of measuring the distance from either end, at which the
factor lies. Photomicrograph after Foot and Strobell.]
Such is the essence of Mendelism; and the reader is probably ready to
admit that it is not a simple matter, even when reduced to the
simplest terms. To sum up, the principal features at the base of the
hypothetical structure are these:
1. There exist relatively constant units in the germ-plasm.
2. There are two very distinct relationships which these units may show
to each other. Two (or more) unit factors may be alternatives in the
mechanism of inheritance, indicating that one is a variation (or loss)
of the other; or they may be independent of each other in the mechanism
of inheritance.
3. The mature germ-cell contains a single system of independent factors
(one representative from each set of alternates).
The immature germ-cells, and body-cells, have double systems of
independent factors (two from each set of alternatives).
4. The double system arises simply from the union of two single systems
(i. e., two germ-cells), without union or even contamination of the
factors involved.
In the formation of a single system (mature germ-cells) from a double
(immature germ-cells), pairs of alternates separate, passing into
different germ-cells.
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