1. Understanding of chromosome
behaviour in mitosis
ALBIO9700/2006JK

2. ALBIO9700/2006JK

3. • Interphase
– DNA only visible as indistinct mass of chromatin.
Nucleolus and nuclear membrane still intact.
Centrioles lie close to one another. DNA undergoes
replication.
• Early prophase
– Chromosomes start to coil up (spiralisation)
becoming shorter and thicker. They become visible
because they stain more intensely. Centriole
replicates just before prophase.
• Late prophase
– Nuclear envelope ‘disappears’ (it breaks up into small
vesicles which are not visible with a light microscope).
Nucleolus ‘disappears’ (forms part of several
chromosomes). 2 chromatids, held together at the
centromere, make one chromosome. Centrioles
move to opposite ends (poles) of nucleus, forming a
spindle of microtubules.
ALBIO9700/2006JK

4. • Metaphase
– Chromosomes line up across the equator of the
spindle. They are attached by the kinetochore on
the centromeres to the spindle. Each centriole
reaches a pole. They help to organise production of
the spindle microtubules.
• Anaphase
– Chromatids move to opposite poles, centromeres
first, pulled by the microtubules.
• Telophase
– Chromatids have reached the poles of the spindle.
They will uncoil again to form chromatin. Spindle
breaks down. Re-forming of nucleolus and nuclear
envelope. Cytokinesis occurs (division of cytoplasm
and cell into two by constriction from the edges of
the cell)
ALBIO9700/2006JK