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Cell Division:
MITOSIS
Genes and Chromosomes
• Humans have 46 chromosomes in all body
cells (somatic cells)
• You have 23 pairs of homologous
chromosomes
– The two chromosomes in the pair look similar
and contain genes which affect the same
characteristics (2 different alleles)
• All of your somatic cells are diploid—they
have chromosomes which are in
homologous pairs
• Some cells don’t have any DNA at all
– Red blood cells
Anatomy of a Chromosome
Check your Understanding
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How many chromosomes do human cells have?
How many pairs of chromosomes do human cells have?
What are somatic cells?
You have one gene for blue eyes and one gene for
brown eyes.
– Where did these genes come from?
– What are the 2 forms of this gene called?
What does diploid mean?
What are the two halves of a single chromosome called?
What structure holds the chromatids together?
What is a gene?
How Eukaryotic Cells Divide
• Cell spends most of its time in interphase
–not dividing, just doing its job
– DNA is stretched out into long, thin chromatin
strands
• Before division, each chromosome is
copied exactly—replication
• Nucleus divides and each daughter cell
gets a full set of chromosomes
– This is called mitosis
Stages of Mitosis
• Prophase
– Chromosomes become visible as they coil up
and get shorter and thicker
– Nuclear membrane disappears
– Centrioles move to opposite sides of the cell
– Spindle fibers appear and shoot out from
centrioles
• Metaphase
– Chromosomes line up in center of cell
– Spindle fibers attach to each chromosome
• Anaphase
– Sister chromatids are pulled apart
– Chromatids are reeled to opposite sides of the
cell by spindle fibers
• Telophase
– Nuclear membrane appears around each set
of chromosomes
– Chromosomes unwind and go back to being
chromatin
Cytokinesis
• Whole cell divides in half
• Each daughter cell has an exact duplicate
of the DNA
• Each daughter cell has 46 chromosomes
• Each daughter cell is diploid—23 pairs of
chromosomes
Check your Understanding
• How are the terms DNA, chromatin, chromosome,
and genes related?
• What is the name of the process by which DNA is
copied?
• Name, in order, the 6 stages of the cell cycle, starting
with the phase cells are in most of the time
• Name the phase of the cell cycle where:
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Chromosomes line up in the middle of the cell
Chromosomes first become visible
Spindle fibers first appear
Spindle fibers attach to sister chromatids
Centrioles move to opposite sides of the cell
Sister chromatids get pulled apart
Still checking…
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Nuclear membrane disappears
Nuclear membrane reappears
Entire cell divides in half
No chromosomes are visible
• How many daughter cells are created from
one parent cell?
– How many chromosomes does each daughter
cell have?
– How many pairs of chromosomes does each
daughter cell have?
– What is the ploidy of the daughter cells?
1: interphase
2: late interphase /
beginning prophase
3: early prophase
4: mid prophase
5: late prophase
6: metaphase
7: late metaphase / early anaphase
8: anaphase
9: early telophase
10: late telophase / cytokinesis
VOCABULARY TERMS
Somatic
Homologous
Alleles
Diploid
Centromere
Gene
Chromatid
chromosome
Interphase
Chromatin
Replication
Daughter cells
Mitosis
cytokinesis