EXTREMES OF SIZE 



8i 



uniform effect on the whole chromosome complement, although it 

 is probably determined by a gene mutation which is itself invisible 

 and strictly local in origin. The first is described as structural or 

 numerical change according as it affects the internal arrangement, 

 the structure, of a chromosome or the number of different 

 chromosomes present. The second is described as genotypic 

 change. When the chromosome complements of living organisms 

 as a whole are compared, their variation is found to be such as can 

 be described in terms of these two kinds of change. 



The time has not yet come when their relative importance can be 

 accurately assessed except in considering small groups of species. 

 An internal and external comparison of the chromosome 

 complements, however, indicates the part played by the two 

 kinds of change. Differences within a chromosome complement 

 indicate solely the range of structural change. Differences in the 

 diameter of the chromosomes in different species indicate solely the 

 range of genotypic change. 



Most complements are uniform in the size of their members, 

 which do not vary over a range of more than two to one. 

 Exceptionally a much higher range of variation is found, reaching 

 a maximum of 500 : i in the domestic turkey, Meleagris (Werner, 

 1931). 



Table 9 



Organisms with an Extreme Range of Size in the Chromosomes 



[cf. Chiasma Frequencies, Ch. VII) 



Plants (Monocotyledons) 



Eucomis hicolor . 

 Yucca filamenlosa 



Morinaga 



Y.flaccida . 

 Agave sisalana 

 Muscari latifolmm 

 Uvularia grandiflora 

 Fourcroya altissima et al. 

 Ornithogalum pyramidale et al 



Miiller, 191 2. 

 Taylor, 1925 c 



et al., 1929. 

 O'Mara, 1931. 



Suto, 1935 ; Doughty, unpub. 

 Delaunay, 1926. 

 Belling, 1926. 

 Heitz, 1926. 

 Heitz, 1926 ; Matsuura and 



Suto, 1935. 



