STCDIES ON THE GENETICS OF FLOWEIt-COLOURS, ETC. 115 



theiiveticiil.' So it is clejii" tlmt we liuvo Iiero t<j deal Avitli a ciise of liukji^e 

 lieloiiging fc) eitliei' uue oi tlie two above series oi* at least to some seiües 

 similar to it. 



To snm up : tlie cross icagenfax x orange has segi-egated in F. in tin; 

 ratio of 3 magentas and 1 orange, because JB and B are completely linked 

 together.; in /•', the linkage became partial in some magentas, and coaseqnently 

 their /''-of&priug contain reds besides magentas and oranges. 



If we will adopt the clu'omosome theoi-y of Morgan we have, for instance, 

 the gametes Clili, CJih, Ci'B, Ci'b in the ratio 5-5 : 1 : 1 : 0-5 (.3-0 being 

 the average of ö and G in the two series of linkage above cited\ and 

 cDns'iqnently lö'4% cross-ovei-s and 84-G% non-ci-oss-overs i"espectively.'- The 

 following consideration may then be made. The factoi-s JB and J5 are 

 located very near in the same clu'omosome, and consequently closely linked 

 together as the rule. But sometimes the crossing-over takes place, so that 

 they come to lie in two dilieront, though homologous, chromosomes, the ratio 

 of ci-oss-ovei-s against non-cross-overa being foimd to be 15'4 : 84-G. 



Tlie facts which pjint out towards tliG variation of the linkage ratio of 

 certain factoi-s have been sometimes observed till now. To cite some instances, 

 Gregory in his researches on Primula sinemis, has found in the i^.-oflspring 

 ex JlsxniS (magenta and long-styled by red and shfjrt-stj'led) the complete 

 linkage between JI and -S', wlier(?as in those ex MS x ins (magenta and short 

 by red and long) the partial one belonging to the series 7:1:1:7 has been 

 observed between the same factoi-s.' Baur, in his' espsrimeuts in Antirrhinum 

 mojtts, has foimd in the i^i-oflspring ex FJTGGxffgg (red and piduratura 

 flower by non-red and non-piduratum) that the linkage ratio between F (red) 

 and G {pidurohtm) is variable in different cases (3:1:1:3, 4:1:1:4, 

 7:1:1:7, or even 1:1:1:1, i. e. normal).' In Lalhjrus odoruius BatesON 



1 S. Peat.sox, TaUes for Slatislicians nnd Biiometrki/tns, Cambriilge, 1914, Table XII. 



- If we calculate the linl<age ratio according to the formula! of Emerson (Amer. N.itur- 

 nlist, Vol. 50, 1916, pp. 1411-1129) we have from the corrected iihitnotypio ratios CRB : 

 CK&: ('»-iJ: CV& = 178-75:20:29:dG25 (from the actual 181 : 20 : 20: 64^-20=181 : 20 : 20 : 44) 

 »•=6'89 and .s = l-34 and consequently the linkage ratio = r/.s = 50 : 1. 



' Journ. of Genetics, Vol. 1, 1911, p. 129. 



* Zeitsch. f. iml. Ahstamm. n. VererUm-js'chre, Bd. f>, 1012, p. 201 ff ; and Eitüeltung in die 



