208 GENETICS IN RELATION TO AGRICULTURE 
homozygous for grossulariata, therefore (LZ)(LZ), and half heterozygous 
(LZ) (IZ). Of the females half are grossulariata W(LZ) and half lacticolor 
W(iZ). Wo lacticolor males are produced in this generation, but they 
may be obtained from matings of heterozygous grossulariata males (LZ) 
(1Z) with lacticolor females W(IZ). The reciprocal cross requires no 
special explanation, since it is perfectly clear from the diagram just how 
the lacticolor factor is transmitted in such cases. Throughout, the whole 
set of experimental evidence duplicates exactly the relations found to 
exist for the inheritance of white eye color in Drosophila except that the 
sex relations are reversed. 
The cytological relations in Abraxas do not appear to rest upon as 
firm a basis as those in Drosophila. Apparently there are normally 56 
chromosomes in both the male and female, and no pair are obviously 
unequal in either sex. Apparently then the W-chromosome in the female 
is about the same size as the homologous Z-chromosome, but like the 
Y in Drosophila it is a neutral chromosome, 2.e., it carries none of the 
dominant sex-linked factors. 
Some additional cytological evidence is provided by examination 
of lines giving aberrant sex ratios. Doncaster discovered certain strains 
in which some of the females gave only female offspring, others only a 
few sons, and still others the normal 1:1 ratio. In these strains the 
males had 56 chromosomes, but the females only 55. As Bridges points 
out, if 56 is the normal chromosome number for the females of Abraxas, 
then those females having 55 chromosomes may be regarded as of the 
ZO type, corresponding to the XO males in non-disjunctional strains of 
Drosophila. Such females produce eggs some with 27 and others with 
28 chromosomes. If as Doncaster’s early observations seemed to show, 
the odd chromosome ordinarily is included in the polar body, then the 
eggs would contain mostly 27 chromosomes, and these on fertilization 
would give 55 chromosome zygotes, presumably females of the ZO type. 
Later observations of Doncaster’s, however, do not confirm the conclusion 
that 27 chromosome eggs are more frequent than those containing 28 
chromosomes. Moreover, although this is perhaps not a very weighty 
argument, it is not clear why ZO females in Abraxas, if such exist, should 
not be sterile like their counterparts, the XO males in Drosophila. 
It is of considerable interest that exceptions in the transmission of the 
sex-linked character lacticolor occur in Abraxas just as they do in Dro- 
sophila. The mating grossulariata female by lacticolor male should give 
only lacticolor females and grossulariata males. However, Doncaster 
found among 611 females, the offspring of 27 such matings, three gros- 
sulartata females and two of these were in the same brood. Assuming 
that the two which were in one brood represented cases of secondary 
non-disjunction, it would appear that primary non-disjunction in Abraxas 
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