The existence of other chiasmata may give rise to more complicated 

 situations or eliminate the effects of the first one, depending on where 

 they occur and what strands are involved. In the case of a pericentric 

 inversion, the position of the kinetochore may be so altered as to change 

 the relative lengths of arms to a detectable degree (Figure 8-4, B); 



# 



V 





Figure 8-5. Photomicrograph of First Meiotic Anaphase of Podophylliiin 

 peltatmn, showing bridge and fragment as a result of crossing over within 

 a region heterozygous for an inversion. 



where there is loop pairing and a single chiasma in the loop, no bridge 

 and fragment results at first anaphase, but instead a pair of deficiency- 

 duplication chromatids, which are identical at the two ends (Figure 

 8-4, B). Pericentric inversions are therefore not as easily diagnosed at 

 first anaphase, unless the lengths of the two chromatids of an anaphase 

 chromosome are detectably different. This, together with the statistically 

 low chance of including any particular point in an inversion, may account 

 for the comparatively low frequency of pericentric as opposed to para- 

 centric inversions. 



184 / CHAPTER 8 



