42 



BIOLOGIC BASIS OF SEX 



instead of 56. At least one of the extra 

 chromosomes is an X. From these observa- 

 tions Love (1957) concluded "detailed stud- 

 ies and comparisons of the sex chromosomes 

 and their pairing in natural and experi- 

 mentally produced polyploids lead to the 

 conclusion that the sex mechanism in this 

 group must be based on the evolution of a 

 strong male determinant in the Y chromo- 

 some, of much the same kind as in Melan- 

 drium, but stronger." 



Within this one genus, Rumex, species are 

 present which seem to have the male de- 

 termining elements (a) located in the auto- 

 somes as in Drosophila, and (b) in the Y 

 chromosomes as in man. When contrasted 

 with the female-determining elements of the 

 X chromosome these male elements seem 

 to vary in their sex-determining capacity 

 in the different species. 



C. SPINACIA 



Spinach is dioecious l)ut the X and Y 

 •chromosomes are cytologically indistin- 

 guishable from each other in at least some 

 species. Spinacia oleracea has 6 chromo- 

 some pairs. Recent work on sex-determining 

 mechanisms for this species has been con- 

 ducted by Bemis and Wilson ( 1953) , Janick 

 and Stevenson (1955a, b), Dressier (1958), 

 and Janick, Mahoney and Pfahler (1959). 

 Dressier has indicated that each pair of the 

 6 chromosomes can be identified by different 

 morphology although most other investi- 

 gators have been unable to make these 

 separations within their own material. He 

 assigns the role of sex differentiation to 

 the chromosome pair having the largest 

 size. The Y chromosome bears a satellite, 

 whereas the X chromosome does not. Janick 

 and Ellis (1959) located the sex chromo- 

 some pair through the use of the six primary 

 trisomies each of which is differentiated 

 morphologically. These trisomies have been 

 obtained as progeny from triploid pistillate 

 XXX bred to diploid staminate XY. Five of 

 the crosses between staminate plants of the 

 six trisomies mated with pistillate diploids 

 gave the one male to one female sex ratio 

 indicative of independence of the sex com- 

 plex from the particular trisomies. The sixth 

 cross utilizing the reflex trisomic gave a one 

 male to two female ratio indicative of the 

 sex complex being within the chromosome 



pair which in triploid condition showed the 

 reflex type. Each of the morphologic triso- 

 mies was associated with one of the six 

 chromosomes. The chromosome associated 

 with reflex trisomic, the sex chromosome, is 

 the longest chromosome and is characterized 

 by submedian centromere. In the somatic 

 cells Janick and Ellis were unable to ob- 

 serve obvious heteromorphism in this 

 chromosome pair. These results, although 

 not agreeing in detail with those of Zoschke 

 (1956) and of Dressier (1958) confirmed 

 the existence of races which differ with re- 

 spect to morphology of the chromosomes 

 containing the XY factors. Janick and 

 Stevenson (1955b) considered that the 

 monoecious character did not depend on 

 unaltered balance between the X and Y 

 factors but seemed to be caused by an allele 

 as well as by other modifying genes. They 

 found that in polyploidy the sex expression 

 in spinach indicated that a single Y factor 

 was male-determining even when opposed 

 by three doses of the X. In their results only 

 the XX, XXX, and XXXX formed pistil- 

 late flowers, whereas the XY, YY, XXY, 

 XXXY, and XXYY were of the staminate 

 type. Extra doses of the Y may have fur- 

 ther effects as illustrated by the fact that 

 YY plants do not produce seed, whereas 

 sometimes the XY staminate progenies ob- 

 tained from selfing staminate plants do, 

 indicating that staminate plants come to 

 their fullest expression with the YY geno- 

 type. Chromosome recovery in the progeny 

 from crosses of 2N females mated to 3N 

 (XYY and XXY) males revealed that the 

 functional gametes from staminate triploids 

 were not confined to N and N 4- 1 types 

 (Janick, IVIahoney and Pfahler, 1959). The 

 progeny produced contained 49 per cent 

 diploids, 18 per cent trisomies, 0.5 per cent 

 14 chromosomes, 1.2 per cent 16 chromo- 

 somes, 11 per cent 17 chromosomes, 19 per 

 cent triploids, and 0.8 per cent 19 chromo- 

 somes. The reciprocal cross in which the 

 female was of the 3N type and the male 

 2N gave distinctly higher ratios of ancu- 

 ploids. Of the progeny, 28 per cent were 12 

 chromosomes, 36 per cent were 13, 7 per 

 cent wTre 14, 0.9 per cent were 15, 2.8 per 

 cent were 16, 13 per cent were 17, 13 per 

 cent were 18, or 60 per cent of the total 

 progeny were aneuploids, whereas in the 



