FOUNDATIONS FOR SEX 



53 



colchicine made the studies more attractive 

 by increasing the numbers of usable cells 

 that were in the metaphase of cell division. 



Ford and Hamerton (1956) in an inde- 

 pendent investigation, closely following 

 that of Tjio and Levan, observed that the 

 human cell complement contained 46 chro- 

 mosomes. They, too, agreed with Painter 

 and others that followed him that the male 

 was XY and the female XX in composition. 

 A flood of confirming evidence soon fol- 

 lowed: Hsu, Pomerat and Moorhead (1957), 

 Bender (1957), Syverton (1957), Ford, 

 Jacobs and Lajtha (1958), Tjio and Puck 

 (1958), Puck (1958), Chu and Giles (1959), 

 and a number of others. 



In most instances the results of the dif- 

 ferent investigators were surprisingly con- 

 sistent in showing that the individual cell 

 chromosome counts nearly always totaled 

 46. This was no doubt due in part to the 

 desirability of single layers of somatic cells 

 for identifying and separating the different 

 chromosomes into distinct units. Chu and 

 Giles' results illustrate this consistency. 

 For 34 normal human subjects, including 

 29 American whites and 4 American Ne- 

 groes, and one of unknown race, and re- 

 gardless of sex, age, or tissue, the diploid 

 chromosome number of the somatic cells 

 was overwhelmingly 46. In only five indi- 

 viduals were other numbers observed in 

 isolated cells. Out of 620 counts, 611 had 

 46 chromosomes; two individuals, whose 

 majority of cells showed 46, had 3 cells with 

 45 chromosomes; three other individuals, 

 the majority of whose cells showed 46, had 

 6 cells with 47 chromosomes. Average cell 

 plates counted per individual was nearly 20. 



The only recent observations at variance 

 with these results were those of Kodani 

 (1958) who studied spermatogonial and 

 first meiotic metaphases in the testes from 

 15 Japanese and 8 whites. In these studies 

 at least several good spermatogonial meta- 

 phases in which the chromosomes could be 

 counted accurately, and secondly at least 

 15 spermatocyte metaphases in which the 

 structure of individual chromosomes could 

 be observed clearly, were made on each 

 specimen. The numbers of cells studied in 

 metaphase were generally above these num- 

 bers, one reaching 60 metaphases. Some var- 

 iation was noted within individuals. Among 



individuals, numbers of 46, 47, and 48 were 

 observed. Among 15 Japanese, 9 had 46, 1 

 had 47, and 5 had 48 chromosomes, whereas 

 among the whites 7 had 46, and 1 had 48. 

 Sixteen of the 23 individuals had 46 chro- 

 mosomes. Karyotype analyses indicated 

 that the numerical variation was caused by 

 a small supernumerary chromosome. On the 

 basis of these observations it would appear 

 that individuals within races may vary in 

 chromosome number and yet be of normal 

 phenotype. However, in view of the exten- 

 sive observations by others, it seems un- 

 likely that the variation between individ- 

 uals is as large as that indicated. It will 

 require much further study to establish any 

 other number than 46 as the normal karyo- 

 type of man. This is particularly true in 

 view of the work of Makino and Sasaki 

 (1959) and Alakino and Sasaki cited by 

 Ford (1960), in which they studied the hu- 

 man cell cultures of 39 Japanese and found 

 without exception 46 chromosomes, and the 

 earlier work of Ford and Hamerton (1956) 

 on spermatogonial material where they, too, 

 found 46 chromosomes in that tissue. The 

 best features of these human chromosome 

 studies will come in the identification of 

 the individual chromosomes making up the 

 human group. The chromosome pairs may 

 be ordered according to their lengths. The 

 longest chromosome is about 8 times the 

 length of the smallest. The chromosomes 

 may be classified according to their centro- 

 mere positions. The chromosomes are said 

 by most observers to be fairly easily sepa- 

 rated into 7 groups. Separation of the indi- 

 vidual chromosome pairs from each other 

 and designation of the pairs so that they 

 can be identified by trained investigators 

 in all good chromosome preparations is not 

 possible according to some ciualified cytolo- 

 gists and admitted difficult by all students. 

 However, standardized reporting in the 

 rapidly growing advances in human cell 

 studies should refine observations, reduce 

 errors, and encourage better techniques. 

 With this in mind, 17 investigators working 

 in this field met in Denver in 1959 in what 

 has come to be called the "Denver confer- 

 ence" (Editorial, 1960). From an examina- 

 tion of the available evidence on chromo- 

 some morphologies an idiogram was set up 

 as a standard for the somatic chromosome 



