Decembee 23, 1921] 



SCIENCE 



635 



porary end to end fusion of certain bivalenits, 

 usually the shorter ones, but occasionally the long- 

 est being involved. This phenomenon is also likely 

 to disturb Mendelian ratios, causing partial linkage. 



This last statement points out clearly the 

 possibility of just such apparently irrecon- 

 cilable results as we have obtained in tlie case 

 of these two rabbits. If English spotting and 

 dilution have their genes located in different 

 chromosomes, the two characters will not 

 ordinarily show linkage. If, however, these 

 two chromosomes should form a temporary 

 union with each other in the spermatogenesis 

 of a male rabbit, linkage would result. Such 

 linkage, however, would not be of the same 

 nature as that found in Drosophila. Its 

 sti'ength would not be due to the distance 

 apart of genes in a chromosome, but to the 

 persistency of the temporary attachment be- 

 tween chromosomes ordinarily distinct. 



The cytology of the rabbit is said to be 

 difficult. Even the number of the chromo- 

 somes has not been definitely determined. 

 According to the summary of Miss Harvey,^ 

 recent observers give the number as 11 or 12 

 pairs, but in older investigations the number 

 is put at 14-18 pairs. One source of un- 

 certainty as to the number may be the forma- 

 tion of temporary attachments between chro- 

 mosomes such as Gates and Eees describe 

 for Laciuca. "While we await the outcome 

 of the study of other cases, it seems reason- 

 able to assume that the two characters, Eng- 

 lish spotting and dilution, have their genes lo- 

 cated in distinct chromosomes, even though 



these may occasionally be united to such an 

 extent as to produce partial linkage in the 

 gametes of certain individuals. 



This case shows the desirability of express- 

 ing linkage strength in terms of something 

 less problematical than map-distances, since 

 linkage may occur which varies quite inde- 

 pendently of map-distance, as for example 

 linkage between genes lying in different chro- 

 mosomes. A method of expressing linkage 

 strength on a scale of 100 has been suggested 

 elsewhere.^ By this method the linkage 

 strength indicated among the gametes of the 

 first rabbit was 23.0 ± 7.26, that for the 

 second rabbit is 0.6 ± 2.7. 



I have recently discovered in rabbits a 

 case of linkage which is not doubtful, since 

 it is found in the gametes of all rabbits so 

 far studied, and in a strength which is be- 

 yond question statistically significant. This 

 involves the same dominant character, Eng- 

 lish spotting, as was involved in the other 

 case. It is strongly coupled with angora 

 coat, a recessive character. The average link- 

 age strength is over 80 on a scale of 100. 

 Table I. summarizes the evidence for this case. 

 In the production of the doubly heterozygous 

 parents used in these test-matings, English 

 and angora were derived one from the father, 

 the other from the mother. Consequently 

 the linkage here takes the form of " repul- 

 sion." The English young are regularly 

 short-haired, the non-English young are reg- 

 ularly long-haired (angora), except in about 

 one case in ten, when a crossover occurs. 



Classes of Young Produced hy Bahhits Doubly Be terozygous for English Spotting and Angora Coat, 

 when Mated with Non-English Sahbits either Homozygous or Heterozygous for Angora Coat 



2 Jour. Morphol, 34, 1920. 



3 Am. Nat., 54, May, 1920. 



