. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 124 GENETICS IN RELATION TO AGRICULTURE Table XXVI.—Linkagk ov Vermilion, SiUiLE, and Hak in Dkosopiiila CJiaraotcTS Gray red normal Gray vermilion normal Sable red normal Gray red bar Gray vermilion Gray vermilion bar. .. Sable red bar Vermilion sable . Non- cross-overs Single cross-overs between Vermilion and , Sable and sable I bar 755 734 724 845 608 800 665 641 110 92 97 87 80 95 81 74 140 151 131 126 123 129 107 108 Double cross-overs Totals 5,772 716 1,015 1 21 9. 53 13,4
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 124 GENETICS IN RELATION TO AGRICULTURE Table XXVI.—Linkagk ov Vermilion, SiUiLE, and Hak in Dkosopiiila CJiaraotcTS Gray red normal Gray vermilion normal Sable red normal Gray red bar Gray vermilion Gray vermilion bar. .. Sable red bar Vermilion sable . Non- cross-overs Single cross-overs between Vermilion and , Sable and sable I bar 755 734 724 845 608 800 665 641 110 92 97 87 80 95 81 74 140 151 131 126 123 129 107 108 Double cross-overs Totals 5,772 716 1,015 1 21 9. 53 13,49 0 2S. Fig. .57.—Diacjcrarn to interference in crossing-over. would protect the loci A, C, and D on either side of it from crossing-over because there would be no close twisting of the chromosomes at these points. As we move on toward E, however, the frequency of double crossing-over would become greater and greater until at E where the modal length of loop was attained double crossing-over values approach- ing those expected on the basis of pure chance would be obtained. Muller has actually shown that such conditions are fulfilled in his twelve-point experiments and he has been al>le to plot a curve showing that the observed frequency of double crossing-over gradually increases until when the modal length is reached the curve coincides with that based on pure chance. Thus we see again how another point of attack has lent support to the conception that the factors are arranged in a linear series and that the hnkage relations of factors are referable to the mechanical consequences of relative positions in the linear series. Bridges points out that interference stands in about the same relation to linkage as linkage does to free Mendelian assortment. Also that the development of the idea of interference is an illustration of the advantage of the chromosome hypothesis. The existence of this phenomenon was Digitized by Microsoft®. Please note that these images
Size: 3331px × 750px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksu, booksubjectplantbreeding
