A ring chromosome is unstable because a break
with reattachment (”crossing-over”) of the
chromatids during the prophase of mitosis usually
leads to difficulties. In this case, a large ringshaped
chromosome with two centromeres
arises during metaphase and telophase. Since
the centromeres migrate in different directions
during anaphase, the ring becomes disrupted. If
this does not occur strictly symmetrically, two
daughter cells will result with certain segments
either missing (deficiency) or duplicated (duplication).
In the example, one daughter cell
with a deficiency of segment 4 and one
daughter cell with a duplication of segment 4
are formed. Not infrequently, ring chromosomes
are lost completely and a monosomy results.
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment