FOUNDATIONS FOR SEX 



55 



complement of the normal human genome. 

 A reproduction of this standard is presented 

 in Figure 1.1, as kindly loaned by Dr. Theo- 

 dore T. Puck for this purpose. 



The autosomes were first ordered in re- 

 lation to their size and such attributes as 

 would help in their positive identification. 

 Numbers were given to each chromosome as 

 a means of permanent identification. Bas- 

 ically, identification is assisted by the ratio 

 of the length of the long arm to that of the 

 short arm; the centromeric index calculated 

 from the ratio of the length of the shorter 

 arm to the whole length of the chromosome ; 

 and the presence or absence of satellites. 

 Classification is assisted by dividing the 

 chromosome pairs into seven groups. 

 Groups 1-3. Large chromosomes with ap- 

 proximatel}^ median centromeres. The 

 three chromosomes are readily distin- 

 guished from each other by size and 

 centromere position. 

 Group 4-6. Large chromosomes with sub- 

 median centromeres. The two chromo- 

 somes are difficult to distinguish, but 

 chromosome 4 is slightly longer. 

 Group 6-12. Medium sized chromosomes 

 with submedian centromeres. The X 

 chromosome resembles the longer chro- 

 mosomes in this group, especially chro- 

 mosome 6, from which it is difficult to 

 distinguish. This large group is the one 

 which presents major difficulty in iden- 

 tification of individual chromosomes. 

 Group 13-15. INledium sized chromosomes 

 with nearly terminal centromeres ("ac- 

 rocentric" chromosomes). Chromosome 

 13 has a prominent satellite on the 

 short arm. Chromosome 14 has a small 

 satellite on the short arm. No satellite 

 has been detected on chromosome 15. 

 Group 16-18. Rather short chromosomes 

 with approximately median (in chro- 

 mosome 16) or sul>median centromeres. 

 Group 19-20. Short chromosomes with ap- 

 proximately median centromeres. 

 Group 21-22. Very short, acrocentric chro- 

 mosomes. Chromosome 21 has a satel- 

 lite on its short arm. The Y chromo- 

 some belongs to this group. 

 Separations of the human chromosome 

 pairs into the seven groups is not as difficult 

 as designating the pairs within groups 

 (Patau, 1960). The svstem is a notable ad- 



vance in summarizing visually the current 

 information in the hope that availability of 

 such a standard will promote further refine- 

 ments, lessen misclassification, and contrib- 

 ute to a better understanding of the problems 

 by cytologists and other workers in the field. 



1. Xuclear Chromatin, Sex Chromatin 



Sexual dimorphism in nuclei of man 

 (Barr, 1949-59) and certain other mammals 

 may be detected by the observable presence 

 of nuclear chromatin adherent to the inner 

 surfaces of the nuclear membrane. The ma- 

 terial is about 1 /x in diameter. It frequently 

 can be resolved into two components of 

 equal size. It has an affinity for basic dyes 

 and is Feulgen and methyl green positive. 

 Nuclear chromatin can be recognized in 60 

 to 80 per cent of the somatic nuclei of fe- 

 males and not more than 10 per cent of 

 males. It is known to be identifiable in the 

 females of man, monkey, cat, dog, mink, 

 marten, ferret, raccoon, skunk, coyote, 

 wolf, bear, fox, goat, deer, swine, cattle, and 

 opossum, but is not easily usable for sex 

 differentiation in rabbit and rodents be- 

 cause these forms have multiple large par- 

 ticles of chromatin in their nuclei. The tests 

 can be made quickly and easily on skin 

 biopsy material or oral smears. Extensive 

 utilization of the presence or absence of 

 nuclear chromatin in cell samples of man 

 has been made for assigning the presumed 

 genetic sex to individuals who are pheno- 

 typically deviates from normal sex types. 

 (See also chapters by Hampson and Hamp- 

 son, and by Money.) Numerous studies on 

 normal individuals seem to support the 

 test's high accuracy. However, in certain 

 cases involving sexual modification, ques- 

 tions have arisen which are only now being 

 resolved. In male pseudohermaphroditism, 

 sex, determined by nuclear chromatin, is 

 male, thus agreeing with the major aspects of 

 the phenotype. For female pseudohermaph- 

 roditism, individuals with adrenal hyper- 

 plasia or those without adrenal hyperplasia 

 give the female nuclear chromatin test. For 

 cases listed as true hermaphrodites Grum- 

 bach and Barr (1958) list 6 of the male type 

 and 19 of the female type. For the syndrome 

 of gonadal dysgenesis they list 90 as male 

 and 12 as female among the proved cases 

 and 15 more as female among those that are 



