. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 168 GENETICS IN RELATION TO AGRICULTURE glabrous, those whites which tinge on fading are hairy and those'which show no sign of coloration on fading are glabrous. The apparent diffi- culty is therefore merely due to the fact that some plants which possess C and R are still white on account of the action of other factors. Altenburg and Muller's Truncate-winged Drosophila.—An even more complicated case of factor interaction is that concerned in the production of truncate wings in Drosophila (Fig. 79).
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 168 GENETICS IN RELATION TO AGRICULTURE glabrous, those whites which tinge on fading are hairy and those'which show no sign of coloration on fading are glabrous. The apparent diffi- culty is therefore merely due to the fact that some plants which possess C and R are still white on account of the action of other factors. Altenburg and Muller's Truncate-winged Drosophila.—An even more complicated case of factor interaction is that concerned in the production of truncate wings in Drosophila (Fig. 79). The factors here involved appear to be the following: ^—a factor for truncate wings. It is a recessive factor located in the second chromosome, and without this factor the truncate wing character cannot appear. ti—a factor which intensifies the expression of the truncate wing character, but which is not absolutely essential. This factor is located in the first chromosome. U—another factor which intensifies the expression of the truncate wing, but is not absolutely essential to it. B'—the dominant factor for bar eyes which in ad- dition acts as an intensifier of truncate. This is a first chromosome factor, line drawing of a ^—a factor for black body color located in the second truncate-wmgcd chromosome. This factor has such an influence that ter Morgan.) flies of the Constitution (bT){bt) or even [Bt){hT) may display the truncate wing character. The truncate wing character was particularly baffling on account of the extraordinary relations which it displayed both in hybridization and in selected strains. In hybridization instead of a 3:1 ratio of long to truncate wing the ratio was about 7:1 and in selected strains even after 100 generations of selection there were still about 5 per cent, of long winged flies. That these long winged flies were different genetically from the truncate winged flies was shown by breeding tests for in such tests they did not produce as h
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