Section 8 — Cytatoxonomy and Experimental Taxonomy 



of chromosomal diversification within each of 

 them. 



8.27. Attempt on the Biological Significance of the 

 Chromosome Numbers. Mihai Serban and 

 Cantemir Riscutia (Bucharest, Rumania). 



In a paper read at the XVI International 

 Congress of Zoology, Washington, 20-27 

 August 1963, we analyzed the distribution of 

 the chromosomes, from the grandparents (P2) 

 in the genome of a certain grandchild (F) using 

 the "indicators of stability" (I.S.), calculated 

 with the formula (1) for even, and (2) for odd 

 numbers of chromosomes. 



Nj 



2 -1 



m 



N/2 



2/2N £ min. C— + 1/2AT. C— ;(1) in which 

 m=o N N 



m + n=N 

 [N/2] m 



2/2N X '«/"■ C — \ (2) in which (N/ 2 ) means 



m=o N 



whole part of N/2 



A table of the I.S. values is given calculated 

 for the numbers N=2-25. We analyzed the 

 distribution of frequency of the haploid chro- 

 mosome numbers (TV) for 2374 species of flower- 

 ing plants (Dobzhansky, 1937) using the I.S. 

 and the values of I.S. generalized for the 

 generations P4 and P6. We found a signifi- 

 cantly greater frequency of numbers N 

 divisible by 8 than by 4, divisible by 4 than by 2, 

 and generally a greater frequency of even 

 numbers compared to odd ones. 



The species in which the interactions between 

 organism and environment are more complex 

 have generally a greater number N, of chromo- 

 somes, which assures a greater stability. The 

 growth of the stability can be explained by the 

 I.S. values, which augment with the increase of 

 N. 



8.28. Chromosomes of Swiss Ants. E. Hauschteck 

 (Zurich, Switzerland). 



Chromosome sets of a number of ant species 

 from the subfamilies Myrmicinae, Formicinae 

 and Dolichoderinae have been investigated. 

 Diploid numbers between 8 and 40 to 50 have 

 been found. The diploid numbers of the Formi- 

 cinae are usually higher than those of the Myrmi- 

 cinae. There is only one genus of the Dolicho- 

 derinae studied which has 22 chromosomes. 

 Species with low chromosome numbers have 



longer chromosomes than species with high 

 chromosome numbers. For instance, Lasius niger 

 has 30 small chromosomes in metaphase, each 

 one to two microns. In Stenamma brevicorne 

 there are only 8 chromosomes but these are five 

 microns or longer. Leptothorax is intermediate. 

 It has 18 chromosomes, each two to six microns. 

 The karyotype of Leptothorax exhibits two 

 striking constrictions on one pair of chromo- 

 somes. In the genus Lasius four species have a 

 diploid number of 30, and one a diploid number 

 of 28 chromosomes. 



8.29. Hybrid Population Analysis by means of 

 Differential Staining of Chromosomes. Humihi- 

 ko Ono, and Bunzo Sakai (Tokyo, Japan). 



Crepidiastrum keiskeanum (Compositae) is 

 distributed along the Pacific coast of southern 

 Japan. In Izu Peninsula, the northern limit of its 

 distribution, many hybrids of this species and 

 some allied ones are found. To analyse the 

 karyotypes of the hybrids, the differential 

 staining method using cold treatment was ap- 

 plied. This treatment reveals special beaded 

 patterns in the chromosomes of Lactuca squar- 

 rosa and faintly staining segments in the chromo- 

 somes of Paraixeris denticulata. In the hybrids 

 each chromosome or its segments are clearly 

 identified. Analysis of minor karyotypes of 

 these hybrids revealed the following extraordi- 

 nary characteristics: 



1. The karyotypes of the hybrids are not 

 always the sum of the genomes of their presumed 

 parents. The maternal chromosomes remain 

 intact in the hybrid karyotypes. Marked dimi- 

 nutions in number and length are often observed 

 in the paternal chromosomes. Many hvbrids of 

 Crepidiastrum keiskeanum (/? = 5) and Lactuca 

 squarrosa (n=9) had 10 chromosomes. But 

 minor karyotypes revealed by the differential 

 staining showed individual differences. 



2. Some of these hybrids were observed to be 

 mixtures of the cells with different karyotypes. 

 Fragmentation and elimination of paternal 

 chromosomes cause the alteration of karyotypes. 

 Such alterations occur among the somatic 

 cells of a single individual. With the lapse of 

 time, cells with the most balanced karyotype 

 overgrow less balanced ones. This phenomenon 

 is ascertained by observing the karyotype of a 

 single plant at different ages and by measuring 

 the pollen fertility of each stem of an individual. 

 The pollen fertility is remarkably divergent 

 according to the position of the stem even in a 

 single plant, although it recovers considerably 

 in successive years. 



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