FOUNDATIONS FOR SEX 



41 



from genetic studies that the occurrence of 

 translocations is responsible for (a) the 

 production of multiple elements from orig- 

 inally single elements, for (b) the frequent 

 change in type of sex chromosome configur- 

 ation in closely related forms, such as in the 

 various species of Rumex and Humulus, and 

 for (c) the associations and non-random 

 segregation of compound elements." The 

 ]n-edictions have been borne out in the com- 

 l)lex chromosomal and genetic systems ob- 

 served in some of the more recent studies. 



Polyploids and trisomies of R. acetosa 

 were studied, particularly by Ono (1935) 

 and Yamamoto (1938). Yamamoto identi- 

 fied each chromosome found in each sex 

 type. He showed that the 6 pairs of auto- 

 somes were not ecjually balanced toward the 

 promoting of the male sex. The chromo- 

 somes called ai , a4 , and ae , had net effects 

 toward the males, whereas chromosome 

 pairs denoted by ao and as had net effects 

 toward female determination. Different bal- 

 ances of the different chromosome types and 

 pairs lead to the production of types named 

 after those of Bridges, supermales, males, 

 intersexes, females, triploids, and superfe- 

 males. 



In his studies of euploid types, Yamamoto 

 set up ratios similar to those used by 

 Bridges in Drosophila, except that he gave 

 the X chromosome a weight of 100 and 

 each set of autosomes a weight of 60. Like 

 Bridges he considered Y chromosome empty 

 of sex genes. By using these weights he was 

 able to arrange the sex types in a consistent 

 series in which the so-called supermales had 

 an index of 0.56, the males 0.83, the inter- 

 sexes 1.11 to 1.43, females 1.67, and super- 

 females 2.50. As in Drosophila the assigning 

 of these different values was handicapped by 

 the lack of any really quantitative measure 

 of the sex evaluations. 



If Yamamoto's carefully tabulated data 

 are assigned 1 for male, 3 for female, 2 for 

 intersex, 3.5 for superfemale, and 0.5 for 

 supermale and then analyzed by least 

 squares for the effects of the different chro- 

 mosomes on sex, the resulting equation is 



Sex value = 1.96 + 1.09 X - 0.1 8Yi 



- O.27Y2 - 0.28ai , + 0.06ao - O.OSa., 



- 0.23a4 + 0.12a.5 - 0.23a6 . 



The X chromosomes contribute a strong 

 female influence and each Y a less effective 

 male influence. The autosomes ai , Sn and 

 ae are somewhat more potent toward the 

 male type than the Y chromosomes. Chro- 

 mosomes &2 , Siz , and as have their sex genes 

 almost in balance. As may be noted, this 

 form of quantitative analysis leads to con- 

 clusions in agreement with those of Yama- 

 moto. 



In another section of the genus, Rumex 

 paucifolms, Love and Sarkar (1956) have 

 analyzed a tetraploid type with 28 chromo- 

 somes. The sex chromosomes were suggested 

 as of the XXXX and XXXY types, the 

 male being heterogametic. The X chromo- 

 somes were the longest whereas the Y was 

 the smallest chromosome in the comple- 

 ment. They concluded that the mechanism 

 of sex determination in this species is de- 

 pendent on the Y chromosome's having 

 strongly epistatic male determinants. This 

 conclusion was based on the fact that the 

 species is dioecious and the belief that the 

 plants are polyploids so that the sex mecha- 

 nism must be based on strong male deter- 

 minants in the Y chromosomes. The strength 

 of these male determinants is suggested to 

 be less than to allow the production of 

 dioecious hexaploids, inasmuch as the tetra- 

 ploid included not only true females and 

 males, but also a low frequency of androgy- 

 nous individuals (Love, 1957). 



In another group of species classified by 

 Love (1957) in the subgenus Acetosella 

 there were 5 species: 2 diploid, 1 tetraploid, 

 1 hexaploid, and 1 octoploid. The diploid 

 species have the XX and XY arrangement. 

 The natural tetraploid, R. tenuijolius, shows 

 about the same degree of pairing at meiosis 

 as do hybrids between it and experimentally 

 produced panautotetraploids of R. angio- 

 carpus. The natural tetraploids show 4 X's 

 or 3X + Y for the females and males. Hexa- 

 ploids derived by alloploidy from the diploid 

 R. angiocarpus and the tetraploid R. tenui- 

 folius have 6 X chromosomes for the female 

 and 5X + Y for the male. Similarly the 

 octoploid R. graminifolius is an autotetra- 

 ploid oi R. tenuifolius with 8 X chromosomes 

 in the female and 7X + Y in the male. Only 

 in this stage do slightly intersexual individ- 

 uals occur as 2N = 57 or 58 chromosomes 



