a single chromosome arm and pericentric, which includes the kinet- 

 ochore (Figure 8-4, A and B). In the former case, with loop pairing 

 and with a chiasma in the loop, the result will be one chromatid with 

 two kinetochores which on separation at first anaphase forms a chro- 



A. When the centromere is 

 outsi de the inversion 



B. When the centromere is 

 within the inversion 



First meiotic anaphase 



First meiotic anaphase 

 c f 



Figure 8-4. Diagrammatic Representation of a Paracentric (A) and peri- 

 centric (B) inversion. (From Srb, A. M. and Owen, R. D., 1955. "General 

 Genetics," W. H. Freeman & Co., San Francisco, Calif., Fig. 10-14, p. 197.) 



matin bridge, and an akinetic fragment which is generally lost (Fig- 

 ure 8-5). Thus the resultant four end products of meiosis consist of 

 two normal cells and two cells having deletions as a consequence of the 

 loss of the fragment. Since the latter two are nearly always inviable, 

 every gamete mother cell so affected will produce only 50 per cent 

 viable gametes. Thus if a chiasma is produced in the inversion region, 

 100 per cent of the time the organism will be only 50 per cent fertile. 



CYTOGENETICS / 183 



