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Unformatted text preview: The as s oc iation of homologous c hromos omes and the effec ts of c ros s ing ov er are us ually s hown in twodimens ional diagrams . This s hort
animation s hows the proc es s in three dimens ions . Hin t 3. What are the requirements and consequences of crossing over?
Cros s ing ov er is unique to meios is . Its oc c urrenc e depends on s pec ific ev ents early in prophas e I and it has important c ons equenc es for the res t of
meios is and bey ond.
Cons ider thes e s tatements about c ros s ing ov er:
1. For c ros s ing ov er to oc c ur, homologous c hromos omes mus t align prec is ely early in prophas e I s o that nons is ter c hromatids c an
ex c hange c orres ponding s egments of DNA.
2. Cros s ing ov er oc c urs at the ends of c hromos omes , rather than near the c entromeres , bec aus e s egments of DNA near the
c entromeres c annot break and rejoin eas ily .
3. As a res ult of c ros s ing ov er, s is ter c hromatids are no longer identic al to eac h other.
4. Cros s ing ov er prev ents homo...
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- Spring '14