The first principles of heredity; with 75 illustrations and diagrms . r reducing divisiontakes place in the nextgeneration, and leaves for thegerm-cell again half the num-ber—, 4A-I-4B. These,combined with 4C + 4D fromthe mother, give us a germ-^ plasm of the composition4A + 4B-1-4C-1-4D. If we re-duce again by half, and soon, we obtain ultimately agerm-plasm consisting of 16different Idants, A, B, C,D, E, F, etc., though in reality this reducing division maynot have taken place so regularly. But this process goes farther still. Not only all theIdants become individually different, but als
The first principles of heredity; with 75 illustrations and diagrms . r reducing divisiontakes place in the nextgeneration, and leaves for thegerm-cell again half the num-ber—, 4A-I-4B. These,combined with 4C + 4D fromthe mother, give us a germ-^ plasm of the composition4A + 4B-1-4C-1-4D. If we re-duce again by half, and soon, we obtain ultimately agerm-plasm consisting of 16different Idants, A, B, C,D, E, F, etc., though in reality this reducing division maynot have taken place so regularly. But this process goes farther still. Not only all theIdants become individually different, but also their Ids. We have already pointed out in a previous chapter thatthe reducing division differs from the ordinary cell-divisionin that it divides the chromatin into two qualitativelydifferent parts. We must now add that this division doesnot necessarily fall between the individual chromosomesor Idants. If we have (see Fig. 39) 4 Idants, A, B, C, D,each with 6 identical Ids—, Idant A with 6 Ids a ;B with 6 Ids h ; C with 6 Ids c ; and D with 6 Ids d—then,. Fig. 39.—Change of Ids(After Delage.) THEORIES OF HEREDITY 67 if we assume them represented diagrammatically in acircle, the division does not necessarily separate each time2 Idants with identical Ids, but may fall near the pointof junction of the Idants, and divide the Idants in suchwise that the new Idants A^, B^, C^, and D^, each have5 Ids of one kind and i of another kind—, A^ =5^+ ic,W =^b-\-ia, O- =^c + id, and T)^=^d+ih. If the samenow happens to the new Idants of the next generation, andso on during many generations, we shall finally get Idantscontaining Ids all of a different character. As each Idrepresents a complete individual, we have therefore in thegerm-plasm represented many individuals of differenttendencies and characters. Furthermore, the reducing division, by removing eachtime one set of chromosomes from the germ-cells, leavesthem with a variety of different chromosomes, so that weget from
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