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appear assortment back-crossed beaded black vestigial cells cent chro chromo chromosome groups conjugation crossing over takes crossover value cytoplasm daughters develop diagram dichete diploid dominant double crossing Drosophila Drosophila melanogaster effect embryo endosperm female fertilized flies four gametes genetic evidence germ-cells germ-plasm give gray gynandromorph half haploid heredity heterozygous homologous chromosomes homozygous hybrid illustrating individuals inheritance kind lethal linkage linked characters linked genes male mate maternal Mendel Mendelian mosomes moth mutant mutant characters normal allelomorph nucleus number of chromosomes occurs offspring pairs of characters pairs of chromosomes parthenogenetic peas plants plastids polar bodies pole present produced race ratio recessive red-eyed relation represent segregation separate sex-chromosome sex-linked shown in Fig species sperm spermatocyte spermatocyte division spermatozoa spindle split sporophyte Sw sW sw synapsis takes place temperature tetrad theory threads tion vinegar fly white eyes white-eyed wild type wild-type wings yellow
Page 9 - EDITORS' ANNOUNCEMENT THE rapidly increasing specialization makes it impossible for one author to cover satisfactorily the whole field of modern Biology. This situation, which exists in all the sciences, has induced English authors to issue series of monographs in Biochemistry, Physiology, and Physics. A number of American biologists have decided to provide the same opportunity for the study of Experimental Biology. Biology, which not long ago was purely descriptive and speculative, has begun to...
Page 226 - ... that at the time of fertilization the hereditary potencies of the two germ cells are not equal, all the early stages of development, including the polarity, symmetry, type of cleavage, and the pattern, or relative positions and proportions of future organs, being foreshadowed in the cytoplasm of the egg cell, while only the differentiations of later development are influenced by the sperm. In short the egg cytoplasm fixes the general type of development and the sperm and egg nuclei supply only...
Page 226 - We are vertebrates because our mothers were vertebrates and produced eggs of the vertebrate pattern ; but the color of our skin and hair and eyes, our sex, stature, and mental peculiarities were determined by the sperm as well as by the egg from which we came.
Page 242 - ... are involved in the production of each organ of the body. It might perhaps not be a very great exaggeration to say that every gene in the germ plasm affects every part of the body, or, in other words, that the whole germ plasm is instrumental in producing each and every part of the body.
Page 242 - The essential point here is that even although each of the organs of the body may be largely a, product of the entire germ-plasm, yet this germ-plasm is made up of units that are independent of each other in at least two respects, viz., in that each one may change (mutate) without the others changing, and in segregation and in crossing over each pair is separable from the others.
Page 241 - ... the individual also; and the viability is lower than in the wild fly. All of these peculiarities are found whenever the white eye emerges from a cross, and are not separable from the white eye condition. It follows that whatever it is in the germ plasm that produces white eyes, it also produces these other modifications as well, and modifies not only such "superficial" things as color, but also such "fundamental" things as productivity and viability.
Page 242 - We find, in experience, that we can not safely infer from the appearance of the character what gene is producing it. There are at least three white races of fowls produced by different genes. We can synthesize whiteeyed flies that are somatically indistinguishable from the ordinary white-eyed race, yet they are the combined product of several known genes.
Page 245 - In this sense, provided it is realized that the sequence is not necessary and may have exceptions it is still possible to employ the words 'cause
Page 92 - The two latter classes are called the crossover classes, or, more briefly, crossovers. The percentage of crossovers is definite for a given stock, of a given age, and under given environmental conditions. In this case the percentages are as follows: Non-crossovers Crossovers Black vestigial Gray long Black long Gray vestigial 41.5 per cent 41.5 per cent 8.5 per cent 8.5 per cent 83 per cent 17 per cent If a pair of chromosomes in the...
Page 9 - It will be the purpose of this series of monographs to emphasize and further as much as possible this development of Biology. Experimental Biology and General Physiology are one and the same science, by method as well as by contents, since both aim at explaining life from the physico-chemical constitution of living matter. The series of monographs on Experimental Biology will therefore include the field of traditional General Physiology.