164 



LIFE: ITS NATURE AND ORIGIN 



, Chromocenter 



H» 



|P 



^lg 



(Spindle Fiber) 



,~^ Diagram of right half of 

 Chromosome 3 



Synapsed 



W,£$^ h \. Unsynapsed 



%* Normal End 3-> 



'^S. Inversion Point - "*" 



V53 Inverted End Chrom. 3" 



Terminal Inversion "C3-l3a" 

 Heterozygote 



Salivary Chromosome 



h 



-50 H 



H 1 — 





H 



31 di (Revised 35a6)C.D.B. 



(94E1) 



Figure 24. (From paper in "Colloid Chemistry," Vol. 5, by J. Alexander, Rein- 

 hold Publishing Corp., N. Y.) 



Figure 23, on which the scale of magnification is indicated, shows 

 in the upper right-hand corner the four pairs of autosomes and 

 the one pair of sex chromosomes as usually seen in cells of 

 Drosophila. The main portion of the figure, at the same mag- 

 nification, shows large size and the wealth of details revealed in the 

 tiny sex chromosomes as found in a salivary gland cell. Figure 



24 illustrates a case wherein a terminal inversion in chromosome 

 3 has prevented complete synapsis of the chromosomes. Figure 



25 illustrates a portion of chromosome 2 where a deficiency (lack 

 of a gene block) has caused an outward looping of the normal 

 chromosome during conjugation. Figure 26 shows a portion of 

 salivary gland chromosome 2 in which the data of the gene maps 



Non-terminal Deficiency 

 "Plexate" heterozygote 



Section involved 



End of Normal 

 Chromosome 2 





Deficiency 



m 



h iom -j 



i i i i i i i i i i i 



34 d 4 (Revised 35 320) C.B.B. 



Figure 25. (From paper in "Colloid Chemistry," Vol. 5, by J. Alexander, Rein- 

 hold Publishing Corp., N. Y.) 





