SECTION 16 



HUMAN CYTOGENETICS 



16.1. (D.) Karyological Evolution in Primates 

 (Catarrhina Monkeys). B. Chiarelli (Torino, 

 Italy). 



The developments of the in vitro tissue culture 

 methods are providing considerable insight into 

 the mechanism of evolution related to chromo- 

 some variations in mammals. 



In this respect some recents works on Primate 

 chromosomes seem very promising. 



During the last four years I had the opportunity 

 of studing the chromosomes of 112 animals, of 

 both sex, belonging to nearly all the species of the 

 Old World Monkeys and Anthropoid Apes. 



The chromosome numbers of these groups of 

 animals show a good deal of variation. 



All the species of the genus Macaca, Papio, 

 Theropithecus and Cercocebus have a diploid 

 chromosome number of 42. Different species 

 differ in some morphological characteristics in 

 their chromosomes. 



All the species I have investigated in the genus 

 Hylobates, Presbytis and Colobus have 44 

 chromosomes and they differ from the others 

 for the morphology of some chromosomes. 



The species Erythrocebus patas has a diploid 

 number of chromosomes of 54. 



In the genus Ceicopithecus the different 

 species have a modal number of 54, 60, 66, 72 

 chromosomes (it is noteworthy that all these 

 numbers are multiples of 6) the morphological 

 differences among the different species are 

 related to the number of acrocentric chromoso- 

 mes. 



All Anthropoid Apes have 48 chromosomes. 

 Some of their chromosomes are different in 

 morphology. 



Moreover in the demonstration I have pre- 

 sented some attempts to interpret the variation 

 in number and morphology of the chromosomes 

 of the different species with centric fusion, inver- 

 sion and translocation mechanisms. 



meiotic and postmeiotic stages. In Locusta 

 migratoria (XO), Mus nuisculus, Rattus norvegi- 

 cus, Mesocricetus auratus, Cricetulus griseus and 

 Homo sapiens up to pachynema typical sex- 

 vesicle structures in early meiotic prophase 

 stages, which include parts of whole sex-chromo- 

 somes, are visible. The heterologous parts and 

 the solitairy X-chromosome of Locusta pass 

 diplonema, diakinesis and metaphase-I in nearly 

 mitotic shape. Entirely heterologous sex-chromo- 

 somes are kept together by an unilateral and 

 achiasmatic end-connection. In Locusta, 54.2 

 per cent of early spermatids (gynospermatids?) 

 own a large Feulgenpositive interphase-structure. 

 which lies in the center of the nucleus. Compa- 

 rable structures with regard to the X- and Y- 

 chromosome are found in the spermatids of man. 

 The sex-vesicle is interpreted as a special 

 structure of allocyclic sex-chromosomes or 

 parts of them, corresponding in early meiotic 

 stages to the chromocenters of mitotic inter- 

 phase-nuclei. So the heterologous parts are 

 protected against crossing-over and allowed to 

 continue in genetic differentiation. As a meiotic 

 attribute an achiasmatic end-connection is 

 formed and the division of the centromeres in 

 metaphase-I prevented. Thus, the meiosis of the 

 heterologous sex-chromosomes may be thought 

 as the scheme of a primitive meiosis, developed 

 secondarily and differentially in the several 

 species. The formation of the sexvesicle is 

 independent of the nucleus-orthoploidy and the 

 DNA-ratio between autosomes and sex-chromo- 

 somes. Heteropycnotic behaviour of sex-chromo- 

 somes in spermatids is interpreted as a condition, 

 capable to block genetic activity, giving equal 

 chances of fertilization to both types of gametes. 



16.3. Studies of Human Pachytene Chromosomes. 



J. I. Valencia, N. Cacheiro and C. Sonnen- 

 schein (Buenos Aires, Argentina). 



16.2. Multilateral Aspects of Meiotic and Postmeiotic 

 Sex-chromosomes in Different Species. Paul 

 Eberle (Gottingen, Germany). 



The X- and Y-chromosomes in the male of 

 different species have been investigated during 



The chromomere pattern of human pachytene 

 chromosomes is being studied, with the purpose 

 eventually of constructing a cytological map. 

 Several bivalents can already by identified 

 tentatively with relation to the mitotic chromo- 

 somes, and some gross chromomere counts have 



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