FOUNDATIONS FOR SEX 



43 



reciprocal cross the value was 31. Aside 

 from some indication of preferential X-YY 

 segregation in the triploid staminate parent 

 when mated to the 2N female, the data fit 

 expectations for the segregations of the Y 

 chromosomes rather well. Staminate flowers 

 were unaffected by such environmental 

 variables as temperature and day length, 

 whereas the monoecious and some pistillate 

 types tended to increase in maleness at the 

 high temperature of 80°F. and short day 

 length (Janick, 1955 L 



D. ASPARAGUS 



Asparagus officinalis plants are ordinarily 

 staminate or pistillate with occasional rudi- 

 mentary organs of the opposite sex appear- 

 ing in both the staminate and pistillate 

 flowers. The staminate and pistillate plants 

 ordinarily represent approximately equal 

 numbers. The rudimentary organs of the 

 male sex sometimes develop and form seed. 

 Rick and Hanna (1943) have showed that 

 when such seeds were planted, 155 males to 

 43 females were produced. The data sug- 

 gested that maleness depends on a dominant 

 gene with the homozygous and heterozygous 

 types indistinguishable. This conclusion was 

 supported by Sneep (1953). The data fur- 

 ther showed that the proportion of stami- 

 nate plants producing seeds was apparently 

 influenced by both heredity and environ- 

 ment, in that seed production in these stam- 

 inate plants was enhanced in some inbred 

 lines but at the same time showed rather 

 wide variability from plant to plant. 



E. HUMULUS 



Humulus sex chromosomes have been 

 identified by Jacobsen (1957) in two spe- 

 cies, H. lupidus and H. japonicus. H. lupulus 

 has a complement of 20 chromosomes in 

 mitosis. The X chromosome is identifiable 

 and separable from the Y chromosome in 

 both mitosis and meiosis. The X chromo- 

 some is longer than the Y but is of medium 

 size compared with the autosomes. H. ja- 

 ponicus has 17 chromosomes in the male 

 and 16 chromosomes in the female at mi- 

 tosis. There are two Y chromosomes Yi and 

 Y2 and an X in the male in both mitotic 

 and meiotic divisions. The female has two 

 X chromosomes. In both species the sex 

 chromosomes in prophase and prometaphase 



are differentiated to show the position and 

 extent of the homologous and differential 

 segments. The Y chromosomes are highly 

 heterochromatic. Based on Ono's 1940 work 

 on triploids derived from crosses of diploids 

 and colchicine induced tetraploids in H. ja- 

 poni'cMs, Westergaard (1958j concludes that 

 the preliminary evidence suggests that sex 

 determination in H. japonicus follows the 

 arrangement of Drosophila in that the X 

 chromosomes are female determining and 

 the autosomes carry the male inheritance. 

 Sex differentiation in other sex dimorphic 

 higher plants follows patterns like those 

 represented by one or another of the plant 

 species discussed above. 



VII. Mating Types 



Species without morphologic sex dif- 

 ferences, which occur as unicellular and as 

 haploid forms, often show differences in 

 their behavioral relations to each other. The 

 types may be alternate. Blakeslee (1904) 

 first called attention to these reactions in 

 heterothallic fungi in which the opposite 

 mating types were so indistinguishable mor- 

 phologically that opposite types were desig- 

 nated as + and — . Preliminary criteria, to 

 be met in assigning the + and — types, 

 were: (1) the individuals studied should be 

 shown to be in fact sexually dimorphic and 

 not merely hermaphrodites or sex inter- 

 grades; (2) tests should include a large num- 

 ber of races in order to show that the dif- 

 ferences are truly related to behavioral 

 differences in reproduction and are not sec- 

 ondary characters peculiar to a race; and 

 (3) the strengths of the reactions should be 

 graded in order to correlate them with any 

 sex differences that might be observed (Sa- 

 tina and Blakeslee, 1925). From more than 

 a quarter century of study, Blakeslee and his 

 group working on some 2000 races included 

 in 30 species of 15 genera came to the belief 

 that over this large group of heterothallic 

 mucors strict sexual dimorphism was the 

 rule. Similar systems have extended the con- 

 cept far beyond this group of fungi. 



In fungi Raper (1960) emphasizes the 

 role of gene differences in the control of sex. 

 Genetic mutations have furnished evidence 

 to show that future sexual capacity follows 

 segregation of genetic factors at meiosis. 

 These factors impose changes in differentia- 



