



Metz and Moses : Chromosomes 



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CHROMOSOMES OF D. AFFINIS AND AN UNNAMED EUROPEAN SPECIES 



Figure 3. Camera lucida drawings of chromosome groups from aceto-carmine "smear" 

 preparations. Numbers 1 and 2 are from an undescribed European species of Drosophila 

 very much life D. obscura. They are metaphases of spermatogonia! cells and represent 

 Type F. Numbers 3 to 10 are from D. a f finis (Type K). 3 to 5 are from spermatogonia! 

 cells and include the full species number of chromosomes, arranged in pairs. 6 to 10 are 

 from the second spermatocytes (which develop into spermatozoa). They include only the hap- 

 loid number of chromosomes — one member from each pair. 6 to 8 represent the X-containing 

 (or female producing) class; 9 and 10 represent the corresponding Y-containing (male pro- 

 ducing ) class. Each chromosome has its characteristic shape and size. In addition to the 

 small dot-like chromosome (not lettered) there are the sex-chromosomes (X and Y), the 

 small rod-like chromosomes (r), the small U- or V-shaped chromosomes (U), and the J- 

 shaped chromosomes (J). In number 9 there appear to be two of the small m-chromosomes 

 present, but one of these may be a granule accidentally carried into the middle of the field. 



was assumed that in willistoni also the 

 rod-Hke pair was the sex-chromosome 

 pair, but this is not the case. By 

 means of non-disjunction it has been 

 shown that one of the large V-shaped 

 pairs is the sex-chromosome pair." 

 Consequently ivillistoni has been put 

 in a new type (M). This suggests 

 that other species included under Type 

 A may also possess V-shaped sex- 

 chromosomes. And it indicates that 

 in comparing types in which the sex 

 chromosomes are not known it is un- 

 safe to assume a correspondence to 

 types in which they are known merely 

 on the basis of general similarities be- 

 tween the groups. 



Characteristics of Individual Chromo- 

 somes 



When the individual chromosomes of 

 the different types are compared it is 

 seen that for the most part they fall 



into three main categories distinguished 

 by size, form, and behavior. These 

 have been described in detail in earlier 

 papers and need only a brief charac- 

 terization here, as follows : 



1. TJic large V-shapcd cliromosomcs, 

 with median constriction and median 

 spindle fibre attachment ; oriented in 

 metaphase with the apex of the V 

 toward the center of the figure. 



2. TJic rod-like ehromosouies, ap- 

 proximately half the length of the V's ; 

 straight, without median constriction ; 

 with terminal spindle fiber attachment 

 and radial arrangement in metaphase. 



3. The in-ehroinosomes, small, dot- 

 like micro-chromosomes, almost in- 

 variably in the center of the field dur- 

 ing metaphase. 



Only two of the thirteen types of 

 groups include chromosomes that do 

 not come under the above headings. 

 These are types E and K. In E 



