Transcript Mitosis & Meiosis

Mitosis & Meiosis
Chapters 8 & 9
Eukaryotic Chromosomes
 Contained
in the nucleus
 The chromosomes replicate to
create two identical chromosomes
that are connected at the
centromere and are called sister
chromatids.
Eukaryotic Chromosomes
cont...
 Chromosomes
are matched in
pairs called Homologous
chromosomes.
 These pairs carry information
for the same traits, are the
same length, and have
centromeres in the same spot.
Eukaryotic Chromosomes
cont...
Although they carry the same
traits they may not code the same
way. (trait = eye color, one codes
for blue eyes and one codes for
brown eyes)
 One of the pair usually comes
from the mom and one comes
from the dad.

Eukaryotic Chromosomes cont...
have 46 chromosomes – 23
homologous pairs.
 Sex Chromosomes– The X & Y
chromosomes in humans, determine
the sex of the individual. XX = girl,
XY= boy
 Autosomal Chromosomes– the
other 22 pairs of chromosomes in a
human. Determine almost everything
except sex in a human.
 Humans
Eukaryotic Chromosomes cont...
A
cell that contains homologous
pairs is considered Diploid (2n).
(46 chromo. in humans)
 A cell that has only one of each pair
(Half of the total chromosomes is
considered Haploid (1n). (23
chromo. in humans)
Eukaryotic Chromosomes cont...
 Germ
Cells– undergo meiosis,
are diploid, but create haploid
cells.
 Egg & Sperm
 Somatic Cells-- undergo mitosis,
are diploid.
 All cells except sex cells.
The Cell Cycle
 The
life cycle of a cell
 Begins
when the cell is formed
and ends when the cell divides or
dies.
The Cell Cycle Cont..
 Stages:


Interphase – divided into three phases.
• G1 Phase (gap period 1)– from birth
until replication begins (time of growth).
• S Phase (synthesis)– DNA is
replicated
• G2 Phase (Gap period 2) – lasts from
the end of DNA replication until the
beginning of cell replication.
Mitosis/Meiosis– cell division
 The
Mitosis
process by which a somatic cell
divides into two identical daughter
cells.
 Phases:
 Interphase
 Prophase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis
Mitosis -- Interphase
 (Not
technically a part of mitosis,
but must occur in order for mitosis
to occur.)
 Chromosomes replicate so that
each chromosome has a sister
chromatid attached to it.
 Cells have twice the number of
chromatids.
Mitosis -- Prophase
condense – coil up
tightly into short thread-like
structures.
 Nucleolus and nuclear envelope
disappear.
 Centrioles move to opposite poles
of the cell and spindle fibers begin
to form.
 Chromosomes
Mitosis -- Prophase

Mitosis -- Metaphase
 Chromatids
line up in the center
of the cell.
 Spindle
Fibers attach to each
centromere.
Mitosis -- Metaphase

Mitosis -- Anaphase
 Centromeres
divide, allowing the
sister chromatids to be pulled
apart and move towards opposite
poles.
Mitosis - Anaphase

Mitosis -- Telophase
 Nuclear
envelopes develop
forming two new nuclei.
 Cytoplasm
and organelles begin
to replicate and divide between
the ends of the cell.
Mitosis -- Telophase

Mitosis -- Cytokinesis
 Cytoplasm
and organelles finish
replicating and the cell divides
into two identical cells.
 Cell membrane forms between
the two cells
 Result: Two Identical Daughter
cells
Meiosis
Germ cells divide to create 4 non-identical
haploid daughter cells.
Phases:
Interphase I
 Prophase I
 Metaphase I
 Anaphase I
 Telophase I

Prophase II
 Metaphase II
 Anaphase II
 Telophase II
 Cytokinesis

Meiosis – Interphase I
 (Not
truly a part of meiosis)
 Chromosomes
replicate
Meiosis -- Prophase I

Chromosomes condense
 Chromosomes pair with their homologous
partner to form tetrads (the four chromatids all
together).
 Crossing over occurs – portions of the
chromatids are exchanged between homologous
chromosomes in order to create genetic
variation.
 Nuclear envelope and Nucleolus disappear
Meiosis -- Prophase I


Meiosis – Metaphase I
 Tetrads
move to the center of the
cell.
 Centrioles move to opposite ends
of the cell.
 Spindle fibers form.
Meiosis – Metaphase I

Meiosis – Anaphase I
 Tetrads
separate (homologous
chromosomes separate, sister
chromatids are still connected.)
Meiosis – Anaphase I


Meiosis – Telophase I
 Chromosomes
are in two groups
at opposite sides of the cell.
 Cell divides into two haploid
cells.
Meiosis – Prophase II
 Chromosomes
both cells.
condense again in
Meiosis – Metaphase II
 Centrioles
move to opposite ends
of the cell.
 Spindle fibers form.
 Sister chromatids line up at the
center of the cell.
Meiosis – Anaphase II
 Centromeres
divide
 Sister Chromatids are pulled to
opposite ends of the cell by
spindle fibers.
Meiosis – Anaphase II
Meiosis – Telophase II
 The
nuclear envelopes of all four
cells form
 Organelles and cytoplasm begin
to duplicate
Meiosis – Telophase II
Meiosis -- Cytokinesis
 Cytoplasm
and organelles finish
replicating and the cell divides
into two.
 Cell membrane forms between
the new cells.
 Four haploid cells are formed.
Mitosis Overview
Meiosis Overview
Which stage is this?
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Which stage is this?
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Which stage is this?
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Which stage is this?
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Which stage is this?