NOTE ON A CASE OF LINKAGE IN PARATETTIX. 



By J. B. S. HALDANE, MA., 



Fellow of New College, Oxford. 



Nabours(I) has shown that the various colour patterns in the 

 grouse-locust, Paratettix texanus, are due to a series of Mendelian 

 factors A, B, C, D, E, F, H, /, J, L, iV", P, Q, and S, which are multiple 

 allelomorphs or else very intensely repelled (this repulsion has been 

 changed to coupling for one pair only), and a factor allelomorphic to 

 its absence only. Nabours regarded this factor as being inherited quite 

 independently of the others. A close examination of his data shows 

 however that in spermatogenesis and any of the other factors exhibit 

 linkage with a cross- over value of about 24 7o or nearly that of the 

 1:3:3:1 system, whilst in oogenesis they exhibit a small linkage, the 

 cross-over value being about 46 °/„. 



The notation used below is that of Nabours, except that the absence 

 of @ is represented in the usual manner by 0, and a zygote known to 

 have been formed from gametes carrying A® and Bd is represented by 

 AS. BO, and so on. In all matings the composition of the father is 

 shown on the left. In Table I are shown the results of Nabours' matings 

 in which the male was doubly heterozygous, and his composition can be 

 determined from that of his parents. Those matings where such a male 

 was mated to a female carrying the same factors are excluded, as we 

 have here no means of determining how much of the observed linkage 

 was due to each parent. Column 1 gives the composition of the parents. 

 Column 2 the number in Nabours' catalogue. Column 3 the total number 

 of young produced, and Column 4 the number of these which were due 

 to " crossing-over " or rearrangement of the factors^ during spermato- 

 genesis. 



For example in Mating 180 the male was of composition A0 . BS, 

 since his parents were ABSd and Ad . S0. When mated to the female 

 Ad.Sdhehegot: 



45 Ae . Ad and A0 . S0, 



17 B0 . A0 „ B0 . S0, 



17.40.^^ „ AS.S0, 



and S1BS.A0 „ B& . 80. 



