Archive image from page 29 of Cytological studies of five interspecific. Cytological studies of five interspecific hybrids of Crepis leontodontoides cytologicalstudi65aver Year: 1930 162 University of California Publications in Agricultural Sciences [Vol. 6 location, deletion, duplication, union, and fragmentation, which have been observed to occur both under natural conditions and after sub- jection to high frequency radiations in Drosophila and Datura. An illustration of the extent of the change in a chromosome com- plement which these processes might produce if operating over long periods
Archive image from page 29 of Cytological studies of five interspecific. Cytological studies of five interspecific hybrids of Crepis leontodontoides cytologicalstudi65aver Year: 1930 162 University of California Publications in Agricultural Sciences [Vol. 6 location, deletion, duplication, union, and fragmentation, which have been observed to occur both under natural conditions and after sub- jection to high frequency radiations in Drosophila and Datura. An illustration of the extent of the change in a chromosome com- plement which these processes might produce if operating over long periods of time is given in figure 18. Here, through the interference of fragmentation, translocation, inversion, deletion, and duplication, a genom has been evolved which differs in chromosome number, size, and shape, from the original complement. Yet the chromosomes of this 'transformed' genom possess segments which are genically sim- ilar to segments of the chromosomes of the original complement. Fig. 18. Diagram showing the possible change in chromosome number and size of a genom brought about through transformational processes. Chromosome segments which are similar in genie constitution in the original and the trans- formed genom are similarly shaded. These segments are now borne by chromosomes of different length and morphology. These processes operating under different external con- ditions over a similar period of time on the same original chromo- some complement would produce transformed genoras of other types, all of which, in common with the two illustrated, would possess seg- ments of chromosomes essentially alike in genie constitution. The similar genes borne by different transformed genoms must be respon- sible for the generic characters common to the species possessing these different genoms. Deletions and duplications of genes, together with gene mutations taking place concurrently with these transforma- tional processes, and not illustrated in the diagram, may in m
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