BIOLOGIC BASIS OF SEX 



Different drugs such as chloralhydrate and 

 particularly colchicine and various forms 

 of radiant ^energy have made it possible to 

 create new types by doubling the chromo- 

 somes, by chromosome rearrangement and 

 by changing the chromosome number. Bet- 

 ter genetic tester stocks of known composi- 

 tion have been organized, which together 

 with a more exact understanding of the in- 

 heritance structure of the species have 

 made for more critical studies. Techniques, 

 which have improved chromosome differen- 

 tiation and structural analysis through bet- 

 ter methods, better dyes, tracers to mark 

 chromosome behavior (Taylor, 1957), and 

 the use of hypotonic solutions in the study 

 of cells (Hsu, 1952), have removed doubts 

 that were created by the earlier technical 

 difficulties. Instrumentation has improved 

 for the measurement, physically and chemi- 

 cally, of cell components. 



D. CHROMOSOMAL ASSOCIATION WITH SEX 



The first genetic linkage groups were as- 

 sociated with the sex chromosomes and 

 were soon shown to follow the patterns of 

 the different chromosome sets observed 

 within the different species. In man, hemo- 

 philia inheritance was observed to follow 

 that which was presumed for the X chro- 

 mosome. Barring in birds and wing-color 

 pattern in Lepidoptera on the other hand 

 were found to follow the chromosomal pat- 

 terns of their species where the male was 

 ZZ and the female Z or ZW for the sex chro- 

 mosomes. The utility of these methods was 

 further probed by Bridges' observations 

 that when chromosome behavior in Dro- 

 sophila resulted in sperm or eggs carrying 

 uncxjx'cted chroiiiosomc combinations there 

 followed ('(nmlly unexpected phcnotypes in 

 the progeny. The cliaractei'istics of these 

 unexpected progeny, in turn, I'ollowt'd those 

 expected if genes for them were carried m 

 the sex chromosomes. The use of these link- 

 age groups as tracers, both as they natu- 

 rally occur and as they may be reorganized 

 through the treatment effects of such agents 

 as radiant energy, open the possibility ol 

 assigning sex effects to, not only chromo- 

 somes, but also to particular i-laces within 

 the chromosomes. 



Both polyploids and aneuploids, as oc- 



curring naturally and as marked by tracer 

 genes, give insight into sex differentiation 

 and its dependence on chromosome inherit- 

 ance behavior. True polyploids in a species 

 are formed as a consequence of multiplying 

 the entire genome. The possible types may 

 have a single set of chromosomes and genes 

 in their nuclei (haploid ) , 2 sets (diploid) , 3 

 (triploid), 4 (tetraploid), and so on, rep- 

 resenting the genomes 1. 2. 3. 4. to whatever 

 level is compatible with life. Multiplying 

 the genomes within the nucleus often in- 

 creases cell size but seldom gives the or- 

 ganism overtly different sex characteris- 

 tics.i Aneuploids, on the other hand, give 

 quite different results, the result being de- 

 pendent upon the particular chromosome 

 that may be multiplied. Particular tri- 

 somies in maize, wheat, and spinach, for 

 example, are distinguishable by marked 

 differences in phcnotypic appearance that 

 is not attributable to cell size but rather 

 to abrupt deviations in particular charac- 

 teristics. The genes in the particular tri- 

 somic set are unbalanced against those of 

 the rest of the diploid sets within the or- 

 ganism. Their phenotypes express these 

 differences. 



E. BALANCE OF MALE AND FEMALE 



DETERMINING ELEMENTS IN 



SEX DETERMINATION 



The foundations for the basic theory that 

 sex determination rests on quantitative re- 

 lationships of two genes or sets of genes 

 localized in separate chromosomes rests 

 largely on tlie work of Morgan, Bridges and 

 Sturtevant, 1910, with Drosophila and the 

 breeding work of Goldschmidt, 1911, with 

 Lymantria. The work of Goldschmidt soon 

 gave extensive descriptions of diploid inter- 

 sexuality in L]imantria dispar. The details 

 of this work scarcely net'd review because 

 they have \)vvn repealed several times and 

 have been smnmarized recently in Gold- 

 schnu(h's Theoretical Genetics (1955). 

 Fioui (hildschmidt's viewpoint, ''the basic 

 point was that definite conditions between 

 the sexes, that is, interscxuality, could be 

 pro.lnced at will l)y proper genetic combina- 

 , tions (crosses of subspecies of L. dispar) 



• The notable exception of the Hynienoptera will 

 I )c discussed later. 



