I.
Chromosomes
A. composed of chromatin – a
complex of DNA and
proteins
B. Homologous chromosomes:
pairs that contain the same
genes, one from each parent
Homologous pair
C.
Chromosomes must be replicated
before cell division.
1. sister chromatids: 2 copies of
the same chromosome
2. connected to each other at their
kinetochores
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II. Why do cells divide?
A. Replacement - cells wear out
& die
B. Repair - tissues can be
damaged by injury or infection
C. Growth of the organism
D. Reproduction
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III. Mitosis
A. New cells are identical to
the old cells
B. Chromosome number is the
same in parent & daughter
cells (diploid – 2N)
C. Growth, repair, & asexual
reproduction
IV.Phases of Mitosis
A. Interphase
1. Growth & normal
cell activities
2. DNA is duplicated
MITOSIS
B.Prophase
1. Chromosomes
condense (sister
chromatids)
2. Centrioles move to
poles
3. Nuclear membrane
dissolves
C.Metaphase
1.Sister chromatids
line up along
equator of cell
2.Chromosomes
attach to spindle
fibers
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2
D.Anaphase
1.Spindle fibers pull
sister chromatids to
opposite ends of cell
**an identical set of
chromosomes moves
to each pole
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E.Telophase
1.Chromosomes uncoil
2.Nucleus reforms
3.Cytokinesis: cell
membrane pinches
in to form 2 separate
cells
MEIOSIS
B.Meiosis
1.Parent cell divides twice to
produce 4 cells
2.Produces gametes (sex cells)
3.Daughter cells have half the
original number of
chromosomes (haploid -1N)
4.When two gametes join to form
a zygote, it will have the
normal # of chromosomes
3
5.Daughter cells are not genetically
identical:
a) Homologous chromosomes
separate, sending one version of
each to the new cells
b) crossing over: sometimes
chromosomal segments are
exchanged between homologous
chromosomes
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V. Phases of Meiosis
A. During meiosis I, homologous
chromosomes are held together
by proteins
1. Interphase I
2. Prophase I
3. Metaphase I:line up next
homologous partner
4. Anaphase I: homologous pairs
separate, sister chromatids
remain together
5. Telophase I
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Meiosis I: (Reduction division)
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Meiosis II: (Mitotic division)
B. Meiosis II
1. Prophase II
2. Metaphase II
3. Anaphase II: sister chromatids
separate
4. Telophase II
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