Interphase before mitosis Before mitosis can begin the
Interphase (before mitosis) • Before mitosis can begin, the nucleus must make a copy of its chromatin so that each new cell will get a complete set of DNA or chromosomes • This is called replication • The chromatin condenses to form double-stranded chromosomes joined in the middle by a centromere • This process is known as interphase
centromere
• Now mitosis can begin • There are 4 stages to mitosis
1. Prophase • Chromosomes are large and condensed • The nucleolus and nuclear membrane break down and begin to disappear • Spindle fibres form from the centrioles
2. Metaphase • The football-shaped spindle is fully formed • The spindle fibres pull the replicated chromosomes into a line across the equator (the middle of the cell) • The chromosomes are attached to the spindle by the centromere
equator
3. Anaphase • The spindle fibres begin to shorten • The centromere is pulled apart • Each one of replicated strands travels to the opposite poles of the cell, along the spindle track
4. Telophase • One complete set of chromosomes is at each pole of the cell • The spindle fibres disappear • Nuclear membranes reform around the chromosomes • The nucleolus reappears • Single-stranded chromosomes start to uncoil into a chromatin formation
• The cytoplasm begins to be divided into two new cells Cytokinesis • In animal cells Ø The cell membrane pinches pinch
animal cells: plant cells:
In REAL cells, what is the MAIN thing that we look for to determine the stage of mitosis? ? v whether or not you can see the chromosomes and how the chromosomes are acting Ø not visible and nucleus intact – interphase Ø visible - late prophase Ø in a line - metaphase Ø Separating - anaphase Ø 2 sets of chromosomes, one at each pole- telophase
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