. Principles of modern biology. Biology. 514 - Heredity and Evolution result if a nucleus fails to divide after the chromosomes have divided, or if two daugh- ter nuclei fuse before the cell divides. Such an aberration occurring in a germ cell may lead to the production of diploid (2m) gam- etes. Such gametes give rise to triploid (3n) offspring if fertilized by normal (n) gametes; or to tetraploid (4?;) offspring if fertilized by other diploid gametes. Both triploid and tetraploid individuals have been found in many species (Fig. 26-29). Tetraploids particularly are apt to be larger than thei
. Principles of modern biology. Biology. 514 - Heredity and Evolution result if a nucleus fails to divide after the chromosomes have divided, or if two daugh- ter nuclei fuse before the cell divides. Such an aberration occurring in a germ cell may lead to the production of diploid (2m) gam- etes. Such gametes give rise to triploid (3n) offspring if fertilized by normal (n) gametes; or to tetraploid (4?;) offspring if fertilized by other diploid gametes. Both triploid and tetraploid individuals have been found in many species (Fig. 26-29). Tetraploids particularly are apt to be larger than their diploid prototypes; and a number of other phenotypic differences may accom- pany the aberration. As to the production of gametes, triploid and tetraploid individuals differ quite mark- edly. Usually all the gametes of a tetraploid are diploid, and all are capable of taking part in fertilization. But the gametes of a triploid individual vary as to their chromo- some count, all the way from n to In, with a majority falling in the intermediate range. And since only the n and 2h gametes can participate successfully in fertilization, tri- ploid individuals are highly sterile. In nature many tetraploid stocks are found among plants, but very few animal tetra- ploids occur. Among cross-fertilizing species there is little chance that both parents should simultaneously produce aberrational (2?;) gametes; and unless this occurs the aberra- tion is almost certain to be eliminated in the next generation, due to the sterility of the triploid offspring. But among self-pollinating plants, a single aberration may reach both the male and female gametes, and thus tetra- ploidy has a fair chance of becoming estab- FLOWERS FRUITS. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marsland, Douglas, 1899-. New York, Holt, Rineha
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