(Figure 4-21). The axis usually appears optically single but there is 

 some evidence that it is at least double. The loops appear to project out 

 from dense regions which are comparable to the chromomeres of other 

 meiotic prophase chromosomes (Figure 4-22). Only the kinetochore, 

 which resembles an enlarged chromomere morphologically, bears no 

 lateral projections. The loops appear to be continuous with the central 

 axis, that is, the axis itself forms the loops (Gall, 1958; Ris, 1957). 



Figure 4-21. Phase-Contrast Photomicrograph of a Bivalent With Ho- 

 mologous Lampbrush Chromosomes Joined by Two Chiasmata in 1st Meiotic 

 Prophase of the Newt, Tritunis cristatus carnifex. Note the numerous lateral 

 loops associated with the central chromosomal axis of each lampbrush 

 chromosome. (Courtesy of Dr. H. G. Callan, The University, St. Andrews, 

 Scotland.) 



The lampbrush chromosomes at maximum development are even 

 longer than the longest salivary gland chromosome, but unlike the latter 

 they are no greater in number of strands than more typical chromosomes. 

 The brush-like characteristic, as noted, reaches maximum development 

 in the late prophase of the first meiotic division (diplotene) and there- 

 after the chromosomes begin to revert to a more typical aspect, until by 

 first metaphase they are quite usual in appearance. While the lateral 

 loops have been shown to contain both protein and RNA, their exact 



102 / CHAPTER 4 



