36 



BIOLOGIC BASIS OF SEX 



mosome the female determining elements. 

 The guiding force of the elements in the Y 

 chromosome during development is suffi- 

 cient to override the female tendencies of 

 several X chromosomes. Data derived by 

 each of these investigators are shown in 

 Table 1.4. 



From these data Warmke (1946) con- 

 cluded that the balances between the X and 

 the Y chromosomes essentially determined 

 sex with the autosomes of relatively little 

 importance. Where no Y chromosomes were 

 present but the numbers of X chromosomes 

 ranged from 1 to 5, only females were ob- 

 served, even though the autosomes varied in 

 number from two to four sets. When a Y 

 chromosome was present the individual was 

 of the male type unless the Y was balanced 

 by at least 3 X chromosomes when an occa- 

 sional hermaphroditic blossom was formed. 



TABLE L4 



Numhers of X, Y, chromosomes and A, autosome sets 



and the sex of the various Melandrium plants 



(Data from H. E. Warmke, 1946; and 



M. Westergaard, 1953.) 



* Occasional staminate but never carpellate 

 blossom. 



t Occasional licrina])hr(i(lit ic blossom. 



When 4 X chromosomes were present to- 

 gether with a Y, the plants were hermaphro- 

 ditic but occasionally had a male blossom. 

 Two Y chromosomes almost doubled the 

 male effect. Two Y chromosomes balanced 

 4 X chromosomes to give a majority of male 

 plants. Only an occasional plant showed an 

 hermaphroditic blossom. Autosomal sex 

 effects, if present, were only observed when 

 plants had 4 sets and 3 or 4 X chromosomes 

 balanced by a Y chromosome. Warmke used 

 the ratio of the numbers of X to Y chromo- 

 somes as a scale against which to measure 

 clianges from complete male to hermaphro- 

 ditic types. No mention is made of quanti- 

 tative measures of the sex character changes 

 with increasing X chromosome dosages. 

 This is of interest since in many forms 

 changes in chromosome balance are accom- 

 panied by changes of phenotype which are 

 unrelated to sex. That such phenotypic 

 changes do accompany changes in autosomal 

 balance in Melandrium are proven, how- 

 ever, by further observations of Warmke in 

 4 trisomic types coming from crosses of 

 triploids by diploids. Of 36 such trisomies 

 analyzed, 5 or 6 of them were of different 

 growth habits and morphologic types. These 

 differences did not affect the sex patterns 

 since all were females. Warmke and Blakes- 

 lee in 1940 observed an almost complete 

 array of chromosome types from 25 to 48 in 

 progeny derived from crosses of 3N x 3N, 

 4N X 3N, and 3N x 4N. Out of about 200 

 plants studied, only 4 were found to show 

 indications of hermaphroditism. These types 

 were 2XY and 3XY. As noted from the 

 table, even the euploid plants would occa- 

 sionally be expected to have an hermaphro- 

 ditic blossom. Of the 200 plants, all with a 

 Y (XY, 2XY, 3XY) were males and all 

 plants without the Y (2X, 3X, 4X) were 

 females. In an 8-year period up to 1946. 

 Warmke was able to observe only one male 

 trisomic. From these facts he concluded 

 that the autosomes are unimportant in the 

 sex determining mechanism utilized by this 

 species. In their crosses they were unsuc- 

 cessful in getting a 5XY plant, the point at 

 which the female factor influence of the X 

 chromosomes might be expected to nearly 

 equal or slightly surpass that of the single 

 Y. From the j^hysiologic side the obscrva- 



