- Created by: Curlot
- Created on: 25-05-15 10:11
The chromosomes start to condense and appear as two chromotids. The chromosomes of each homologus pair lie side by side to form bivalents. The chromatids of each pair become entwined and tension develops at these points called chiasmata. Enzymes may cut the DNA at these points and splicing them back onto the chromatid, this is genetic crossing over. Chiasmata hold the chromosomes together as the drift apart.
During crossing over the chromatids twist around each other creating tension and pieces break off. It will swap over. It can happen more than once, this causes variation to happen.
During metaphase 1 spindles are formed and connect to the centromere. The chromatids align at the centre of the cell. The nuclear envelope disappears.
Chromatids are pulled to opposite poles of the cell (half)
Chromosomes are pulled to either poles and spindles disappear. Sometimes a nuclear envelope forms. Chromosomes stay condensed.
New spindles form at right angles to the old ones. Cross over has happened
Spindles are attached to centrioles and centromeres. The chromosomes are pulled to the equators of the sister chromatids.
The sister chromatids are pulled toopposite poles by the spindles.
Chromosomes elongate and spindles disappear, the nuclear envelope reforms. Cytokinesis occurs and produces four haploids.