FOUNDATIONS FOR SEX 



37 



tion of Strassburger in 1900, as quoted by 

 both Warmke and Westergaard, that the 

 fungus Ustilago violacea when it infects 

 Melandrium will cause diseased plants to 

 produce mature blossoms with well devel- 

 oped stamens (filled with fungus spores) as 

 well as fertile pistils, shows that these fe- 

 males have the potentialities of both male 

 and female development. The case suggests 

 that sex hormone-like substances may be 

 produced by the fungus which acting on the 

 developing Melandrium sex structures 

 cause sex reversions. Should this be true, 

 Melandrium cells would have a parallel 

 with those of fish where sex hormones incor- 

 |)orated in the developing organism in suf- 

 ficient quantities can cause the soma to 

 develop a phenotype opposite to that ex- 

 pected of their chromosomal type. For other 

 aspects see Burn's chapter and Young's 

 chapter on hormones. 



Westergaard's studies (1940) with Euro- 

 pean strains of Melandrium were in prog- 

 ress at the same time as those of Warmke 

 and Blakeslee. In their broad aspects both 

 sets of data are concordant in showing the 

 l^rimary role of elements found within the 

 Y chromosome in determining the male sex 

 and of elements in the X chromosomes for 

 the female sex. Examination of Table 1.4 

 shows that the strain used by Westergaard 

 has a Y chromosome containing elements of 

 greater male sex potentialities than the 

 strain used by Warmke. 



A similar difference appeared in the sex 

 potencies of the autosomes of European 

 strains. Instead of obtaining essentially 

 only male and female plants in crosses in- 

 volving aneuploid types, Westergaard ob- 

 tained from 3N females (3A + 3X) x 3N 

 males (3A + 2XY) 10 plants which were 

 more or less hermaphroditic, 21 females, and 

 15 males. Studies of the offspring of these 

 hermaphrodites through several generations 

 showed that their sex expression required 

 effects by both the X chromosomes and cer- 

 tain autosome combinations which under 

 special conditions counterbalanced the fe- 

 male suppressor in the Y chromosome. In- 

 creasing the X chromosomes from 1 to 4 

 increased the hermaphrodites from to 100 

 per cent in the presence of a Y chromosome. 

 However, in euploids these types would be 



all males. The significance of the autosomes 

 is further shown by the fact that among 205 

 aneuploid 3XY plants, 72 were males and 

 133 were hermaphrodites. 



As pointed out for Drosophila, quanti- 

 tative studies on the effects of sex chromo- 

 somes and autosomes in Melandrium are 

 handicapped by not having a suitable scale 

 for the evaluation of the different sex types. 

 The data presented by Westergaard and by 

 Warmke make this difficulty become partic- 

 ularly evident. In the interest of quantizing 

 the X, Y, and A chromosome on sex the 

 author has assigned a value of 1 for the 

 male type, 3 for the female type, and 2 

 when the types are said to be hermaphro- 

 ditic. When the types are mixed, as for ex- 

 ample, in the data of Warmke where he says 

 a particular type is male with a few blos- 

 soms, the type is assigned a value of 1.05 or 

 1.10, depending on the numbers of these 

 blossoms. His bisexual type which comes 

 as a consequence of Y, 4X and 4A chromo- 

 some arrangement is given a value of 2, al- 

 though possibly the value should be some- 

 what higher as it may well be that the fully 

 bisexuals are further along in the scale to- 

 ward female development than the hermaph- 

 roditic types. The data are treated on the 

 additive scale both as between chromosomal 

 types and within chromosomal type. This is 

 apparently unfair if we examine the work 

 of Westergaard in which it looks as if par- 

 ticular autosomes rather than autosomes in 

 general make a contribution to sex determi- 

 nation. The results, when these methods are 

 used, are as follows: 



Westergaard in Tables 1 to 5 of his 1948 

 paper gives information on sex types with 

 a determination of the numbers of their 

 different kinds of chromosomes. Analysis 

 of these data by least square methods shows 

 that the sex type may be predicted from 

 the equation 



Sex type = - 1.37 Y + 0.10 X 



+ 0.01 A + 2.34 



This equation fits the data fairly well con- 

 sidering that the correlation between the 

 variables and the sex type is 0.87. This 

 analysis again shows that the Y chromo- 

 some has a strong effect toward maleness. 

 The X chromosomes are next in importance 



