FOUNDATIONS FOR SEX 



35 



liave revealed no W chruniosome loci for 

 genes expressed as morphologic traits. From 

 radiation-treated material it has been pos- 

 sible to pick up a translocation of chromo- 

 some II to the W chromosome as well as a 

 cross-over from chromosome Z. This chro- 

 mosome together with tests of hypoploids 

 and hyperploids have materially aided in 

 understanding how the normal chromosome 

 complexes determine sex. The sex types re- 

 sulting from different chromosome arrange- 

 ments have been summarized by Yokoyama 

 1 1959) and are presented in Table 1.3. 



Whenever the W chromosome was ab- 

 sent a male resulted. Extra Z or A chromo- 

 somes did not influence the result. Similarly 

 with a W chromosome in the fertilized egg 

 a female developed. Again extra Z or A 

 chromosomes did not influence the result. 



A full Z chromosome was essential to sur- 

 vival. Hypoploids deficient for different 

 amounts of the Z chromosome in the pres- 

 ence of a normal W chromosome all died 

 without regard to the portion deleted. Hy- 

 perploids for the Z chromosome, on the other 

 hand, when accompanied with a W chromo- 

 some all lived and showed no abnormal sex- 

 ual cliaracteristics. Parthenogenesis led to 

 the pioduction of both sexes, although the 

 males were more numerous than the fe- 

 males. Diploidy was necessary for the em- 

 l)ryo to go beyond the blastoderm stage. 

 Triploid and tetraploid cells were often 

 found. High temperature treatments led to 

 merogony (Hasimoto, 1929, 1934). The ex- 

 ceptional males were homozygous for a sex- 

 linked recessive gene and were explained 

 by assuming that the egg nuclei were in- 

 activated by the high temperature and 

 the exceptional males developed from the 

 union of two sperm nuclei. This conclusion 

 was supported by cytologically observed 

 l)olyspermy (Kawaguchi, 1928) and by 

 cytologic observation of the union of two 

 sperm nuclei by Sato ( 1942 ) . Binucleate eggs 

 were also believed to occur, which when 

 fertilized by different sperm may each con- 

 struct half of the future body. This type of 

 mosaicism was influenced by heredity 

 iGoldschmidt and Katsuki, i927, 1928, 

 1931 ). Polar body fertilization was also be- 

 lieved to occur, one side of the embryo orig- 

 inating from the ordinary fertilized egg nu- 

 cleus and the other side from the union of 



TABLE 1.:^ 

 Sex in Bombyx iitori 

 (Summarized by T. Yokoyama, 1959.) 



nuclei of two of the polar bodies. Similarly, 

 dispermic merogony was noted following 

 the formation of one part of the body from 

 the fertilization nucleus, the other part from 

 the union of two sperm nuclei, the result 

 being a gynandromorph or mosaic. 



VI. Sex Determination in Dioecious 

 Plants 



\. MELAXDRUM t LYCHNIS] 



Over the last 20 years studies on several 

 species of dioecious plants have made not- 

 able advances in unclerstanding the mecha- 

 nisms by which sex is determined. 



Melandrium album has been shown to 

 have the same chromosome arrangement as 

 Drosophila. The male has an X and Y plus 

 22 autosomes, whereas the female has XX 

 plus 22 autosomes. Sex-linked inheritance 

 is known for genes borne in the X chromo- 

 somes as well as for genes born in the Y 

 chromosome. The X and Y chromosomes 

 are larger than any of the autosomes with 

 the Y chromosome about 1.6 times that of 

 the X in the materials studied by Warmke 

 ( 1946) . Separate male and female plants are 

 characteristic of the species. By use of 

 colchicine and other methods, Warmke and 

 Blakeslee (1939), Warmke (1946), and 

 Westergaard (1940) have made various 

 l^olyploid types from which they could de- 

 rive other new X, Y and A chromosome 

 combinations from which information was 

 obtained on the location of the sex deter- 

 mining elements. The Y chromosome carries 

 the male determining elements, the X chro- 



