Interphase –
 Chromosomes are loose in the
nucleus – like spaghetti.
 Too small and thin to be seen by a
microscope.
 Most of the cell’s life (90%) is spent
in Interphase
Prophase
 Chromosomes coil up and replicate themselves, so
there are identical pairs of each of the 46 chromosomes.
 Centrioles begin to move to either side of the nucleus.
 Nuclear membrane dissolves
Metaphase
 Each chromosome lines up in the middle of the cell.
The Spindle Fibers reach out from the Centrioles to
grab each Centromere
 Meta = middle
Anaphase
 Chromosomes are pulled apart, half of each
chromosome goes to opposite sides of the cell.
 Now each side has a perfect copy of each of the 46
chromosomes
 Ana = Apart
Telophase
 A new nuclear membranes forms around each
chromosome bundle.
 Cytokinesis – the cell pinches off in the middle,
creating two cells, each identical to the original cell.
 Called diploid cells – a full 46 chromosome set.
 Cell returns to Interphase
The first six steps are the same as
mitosis with a few exceptions
Prophase 1
 Homologous (matching) chromosomes duplicate and
align with one another.
 There are 23 pairs in all (46 chromosomes)
 Crossing-over occurs between homologous
(matching) chromosomes creating unique version of
each chromosome.
 This allows for more differences in the next generation
Metaphase 1
 SPINDLE FIBERS attach to each chromosome pair at
the Centromeres and the pairs align in the middle of
the cell.
(same as Mitosis except they 23 pairs rather than 46
duplicated singles.)
Anaphase 1
 Chromosome pairs are separated(not torn in two) and
the sister chromatids are moved to opposite ends of
the cell.
Telophase 1
Telophase 1
 New nuclear membranes are formed and the cell
pinches into two cells (Cytokenisis)
 Each cell is genetically unique from all others thanks
to crossing over and random shuffling.
Prophase 2
 In each of the two new cells…
 Nuclear membrane dissolves again
 Centromeres move to the sides and send out spindle
fibres
 The chromosomes move towards the center line of the
nucleus.
 This time, no replication has taken place (The
replication already took place in Prophase I)
Metaphase 2
 Spindle fibers attach to the centromeres of each
chromosome and begin pulling
Anaphase 2
 Chromosomes are pulled apart towards the Centrioles
Telophase 2
 New nuclear membranes form, resulting in 4 haploid
cells
 Haploid means there is ½ the genetic material needed
to make the organism. (23 in humans)
 Haploid cells form a sperm or egg, which will regain
their full 46 chromosomes if fertilization takes place.