. Cell heredity. Cytogenetics. Normal (Bar-reverted). Double-bar Normal FIGURE Comparison of chromosomal segments in Bar-eye and wild-type Drosophila. The segment 16A of the X chromosome consists of a characteristic banding pattern in the wild type, which is present twice in Bar-eye flies, and three times in double-Bar (from Bridges, 1936, Science, 83:210). work of Sturtevant on Bar-eye, a dominant mutation on the X chromo- some in Drosophila. Sturtevant showed that "mutations" from Bar-eye (B) to normal (b) and to an extreme form called double»-Bar (BB) result from unequal cr
. Cell heredity. Cytogenetics. Normal (Bar-reverted). Double-bar Normal FIGURE Comparison of chromosomal segments in Bar-eye and wild-type Drosophila. The segment 16A of the X chromosome consists of a characteristic banding pattern in the wild type, which is present twice in Bar-eye flies, and three times in double-Bar (from Bridges, 1936, Science, 83:210). work of Sturtevant on Bar-eye, a dominant mutation on the X chromo- some in Drosophila. Sturtevant showed that "mutations" from Bar-eye (B) to normal (b) and to an extreme form called double»-Bar (BB) result from unequal crossing-over events. In a cytological study, Bridges found that the Bar phenotype results from repeats of the Bar region; it is present once in the normal, twice in Bar-eye, and three times in double- Bar as shown in Figure Sturtevant compared the phenotypic effects of different numbers of repeats, (including another allele called infra-Bar), when located on the same and on homologous chromosomes. He counted the numbers of facets in the eye and found: Genotype Facets per Eye +/+ 780 B/+ 358 B/B 69 BB/ + 45 B/infra-B 73 Binfra-B/ + 50 infra-B/infra-B 293 infra-B infra-B/-|- 200. 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 Sager, Ruth; Ryan, Francis J. (Francis Joseph), 1916-. New York, Wiley
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