. The elements of genetics. Genetics. THE CHROMOSOME BASIS M P. Fig. 9.—Maps showing the linear distribution of 13 genes and the centromere (cent) in the X-chromo- some of Drosophila melanogaster. C is the map ob- tained by arranging the genes according to the frequencies of crossing-over (as judged by genetic recombination) between them. M is the correspon- ding map where the genes are spaced according to the proportionate rates of occurrence of lethal mutations between them. P is the cytological map based on the positions of the genes in the polytene chromosomes of the salivary glands, and S
. The elements of genetics. Genetics. THE CHROMOSOME BASIS M P. Fig. 9.—Maps showing the linear distribution of 13 genes and the centromere (cent) in the X-chromo- some of Drosophila melanogaster. C is the map ob- tained by arranging the genes according to the frequencies of crossing-over (as judged by genetic recombination) between them. M is the correspon- ding map where the genes are spaced according to the proportionate rates of occurrence of lethal mutations between them. P is the cytological map based on the positions of the genes in the polytene chromosomes of the salivary glands, and S that based on the positions of the genes in the mitotic chromosomes of the nerve ganglia cells. Only 7 of the genes have been localized on the mitotic map. The large block of heterochromatin near the centromere is shown black. It is hardly detectable in the genetic map, and is much smaller in the poly- tene than in the mitotic chromosomes. cent 47. 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 Darlington, C. D. (Cyril Dean), 1903-; Mather, Kenneth. New York : Macmillan
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