40 



BIOLOGIC BASIS OF SEX 



the Y chromosome acted as a positive sup- 

 pressor of female determining regions in the 

 X chromosomes. That these regions were 

 strictly located and the effect not due to the 

 quantities of the Y chromosome which may 

 have been present or absent was indicated 

 by crosses of the different types of frag- 

 ments. In these crosses the resulting total Y 

 chromatin may have been considerably 

 greater in size than a normal single Y chro- 

 mosome, yet the observed changes in sex 

 characteristics of the specific regions lost 

 were present. The results indicated that the 

 sex elements located in the Y chromosomes 

 were qualitatively distinct from one another 

 in their action and cannot be substituted 

 for another in quantitati^'e fashion. The 

 causes of the differential changes in each 

 case could rest on single gene differences or 

 possibly a closely associated nest of such 

 genes. 



Westergaard's studies showed that his 

 plants behaved differently in some particu- 

 lars from those of Warmke. His search for 

 the male determining elements in the Y 

 chromosome of his Danish plants empha- 

 sized these differences. He was able (1946a, 

 b) to divide the Y chromosome into four 

 different regions, a region corresponding to 

 the X chromosome in which there was 

 synapsis and three regions containing vari- 

 ous sex initiating elements. When these ele- 

 ments were compared with those of 

 Warmke's it was found that they were com- 

 parable in action but differed in their order 

 within the Y chromosomes. The Danish 

 l)lants had the female suppressor region in 

 the end opposite the pairing region at the 

 extremity of the differential region. The ele- 

 ments initiating anther development were 

 found near the centromere, but toward the 

 pairing region. The element which com- 

 l)leted development was found near the 

 l)airing region or homologous section. When 

 compared with Warmke's results the i^osi- 

 tion of the different elements in the Wester- 

 gaard material was the reverse of that in 

 the American material. Westergaard ex- 

 plained this difference on the assumption of 

 a centric inversion in the Y chromosome re- 

 sulting in the change of positions. As he 

 suggested, it would certainly be interesting 

 to know the geographic distribution of 



these two types and what would result in 

 progeny of crosses between them. 



Westergaard (1948) summarized his 

 views on the sex-determining mechanism in 

 Alelandrium as follows. A trigger mecha- 

 nism is built up by an absolute linkage be- 

 tween the female suppressor region and at 

 least two blocks of essential male genes in 

 the Y chromosome. This trigger mechanism 

 operates with the X chromosomes and auto- 

 somes in which the X chromosomes have fe- 

 male potencies and certainly the autosomes 

 contribute to them. The action of these two 

 types can only be demonstrated through 

 the breaking of the normal balance by pol- 

 yploidy or aneuploidy. As yet, the female 

 ])otentials of the X chromosome and certain 

 of the autosomes have not been analyzed to 

 the extent of showing whether they contain 

 major female sex genes or flocks of modify- 

 ing genes. W^estergaard favors the hy- 

 pothesis of modifying genes. 



B. RUMEX 



Rumex studies on sex determination took 

 their origin as with most dioecious plants 

 in chromosome examinations of the different 

 members of this genus (Kihara and Ono, 

 1923; Kihara, 1925; Ono, 1930, 1935; 

 Kihara and Yamamoto, 1935). These 

 studies showed that the species Rumex ace- 

 tosa had the normal diploid female comple- 

 ment of 14 chromosomes consisting of a pair 

 of X chromosomes and 6 pairs of autosomes 

 and the male had one X chromosome op- 

 posed by 2 Y chromosomes with 6 pairs of 

 autosomes. Occasionally intersexes found in 

 nature had 2 X chromosomes, 2 Y chromo- 

 somes, and 3 sets of autosomes. Sex deter- 

 mination in this earlier data, as summarized 

 in Tables 3 and 4 of Yamamoto's excellent 

 1938 paper, when analyzed by us utilizing 

 the metliods of least squares, showed tiiat 

 X chromosomes had large female effects in 

 both euploids and aneuploids whereas the 

 net effects of the Y chromosomes and auto- 

 some sets were but one-sixth to one-tenth 

 as great and in the male direction. Since 

 that time great advances have been made 

 through the studies of Yamamoto (1938), 

 Love (1944), Smith (1955), Love and 

 Sarkar ( 1956) , and Love (1957). As Bridges 

 foi'ctold in 1939, "It may now be suggested 



