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CELL DIVISION IN
EUKARYOTES
Professor Andrea Garrison
Biology 11
Illustrations ©2010 Pearson Education,
Inc.
Cell Division
PURPOSE: Reproduction of new cells from
previously existing cells
Cell Division
2
Cell Division of
Genetically Identical Cells
Cell Division
3
Cell Division of
Genetically Identical Cells
Cell Division
4
Cell Division of
Genetically Different Cells
Functions of Cell Division
Production of eggs and sperm for sexual reproduction
Cell Division
5
Cell Division
• When cell divides:
– Membrane pinches in two (cytokinesis)
– Cytoplasm with organelles is divided roughly into
two halves
– Only one nucleus & important to have all genetic
info
• Chromosomes must replicate
• Chromosomes must be divided into two nuclei
– Requires very organized process
Cell Division
6
Nucleus Preps for Cell Division
DNA Replicates, then:
Nuclear preparations for
cell division of
genetically identical
cells
Mitosis
differs from
Nuclear preparations for
cell division of
genetically different
cells
Meiosis
Cell Division
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Cell Division
• Mitosis keeps chromosome number the same
• Meiosis cuts chromosome number in half
Cell Division
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Cell Division
• Both mitosis and meiosis occur in the human
body
• Mitosis occurs in somatic cells
– Body cells that do not give rise to eggs or sperm
• Meiosis occurs in germ cells
– Cells in ovaries or testes that give rise to eggs or
sperm (gametes)
Cell Division
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Mitosis
• Occurs during cell division of somatic cells
• Division of two sets of genetic material
• Insures that both daughter cells have identical
copies of all the mother cell’s chromosomes
(full set of genetic info; one from each parent
= diploid)
Cell Division
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Mitosis
• Genetic information is coded in the
chromosomes
• Different species have different # of
chromosomes
Cell Division
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Cell Division
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Human Chromosomes
Cell Division
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Chromosome
Cell Division
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Chromosome
Cell Division
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Chromosome
Cell Division
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Chromosome
Cell Division
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Somatic Cell Cycle
• 5 phases in life cycle; 4 are part of mitosis
– Interphase
– Prophase
– Metaphase
These 4 phases = mitosis
– Anaphase
– Telophase
–I P M A T
Cell Division
18
Somatic Cell (Life) Cycle
Cell Division
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Somatic Cell Cycle
• Interphase
– DNA is replicating, preparing for mitosis
– G1, S, G2
• 4 phases of mitosis then separate the 2 sets of
DNA in an organized manner
Cell Division
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Interphase
• DNA replicates
inside nucleus
• Centrioles double
Cell Division
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Cell Division
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Mitosis -- Prophase
• Chromosomes
coil
– Become visible
under light
scope
• Nuclear
envelope
dissolves
• Spindle forms
Cell Division
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Cell Division
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Mitosis -- Metaphase
• Chromosomes line
up on equatorial
plane of cell
• Spindle microtubules
attach to
chromosomes
Cell Division
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Cell Division
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Mitosis -- Anaphase
• Microtubules pull
sister chromatids
apart
• Daughter
chromosomes move
towards opposite
poles
Cell Division
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Cell Division
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Mitosis -- Telophase
• Chromosomes reach
opposite poles,
uncoil
• Nuclear envelope
reforms
Cell Division
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Cell Division
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Cytokinesis
• Dividing of cell
into two cells
• Not part of
mitosis
• Occurs towards
end of mitosis
Cell Division
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Cytokinesis
Cell Division
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Mitosis and Cytokinesis in Plant Cells
Cell Division
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Cancer – Mitosis Out of Control
Cell Division
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Meiosis
• Occurs during cell division of germ cells to
produce gametes
• Division of two sets of genetic material twice
– Replicate once, divide twice
• Produces gametes with ½ the genetic info
– One of every chromosome
– Fertilization will double the chromosomes
Cell Division
35
Meiosis
• Humans have 23 different types of
chromosomes
– #1 – 23
– Two of each type
homologs
– Each type carries genes for specific traits
• Eye color, hair color, etc
– Each homolog carries the specific code from one
parent
• Blue eyes, brown hair, etc
Cell Division
36
Human Chromosomes
Cell Division
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What is a “set” of genetic info?
• Somatic cells have two (homologs) of every
chromosome = diploid (2n)
– Human somatic cells have 46 chromosomes
• Gametes have one (homolog) of every
chromosome = haploid (1n)
– Human gametes have 23 chromosomes
Cell Division
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Meiosis
Takes cell with two homologs for each
chromosomes and cuts it to one
homolog for each chromosome
Cell Division
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Meiosis
• Similar to mitosis except
– Single cell undergoes two sets of divisions
– 4 resulting cells are haploid
– Chromosomes contain new gene combinations
due to crossing over
Cell Division
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Meiosis
What’s crossing over?
– Process by which homologs switch pieces of DNA
so each resulting homolog has material from each
of the two initial homologs
Cell Division
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Crossing Over
Cell Division
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Meiosis
• Two sets of divisions
– Meiosis I and Meiosis II
– Meiosis I separates homologs
– Meiosis II separates sister chromatids
Cell Division
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Meiosis
Meiosis I
•
•
•
•
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis II
•
•
•
•
Cell Division
Prophase II
Metaphase II
Anaphase II
Telophase II
44
Meiosis
• Interphase
– Prior to meiosis I
– Chromosomes replicated
Cell Division
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Meiosis I
Cell Division
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Meiosis I
Cell Division
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Meiosis II
Cell Division
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Meiosis
• Result of meiosis is 4 haploid cells
– NOT genetically identical
• Formation of sperm exactly as shown
• Formation of ova (eggs)
– Three disintegrate
– One egg (larger than rest) survives to be released
each month
Cell Division
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Meiosis Mistakes
Cell Division
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Fertilization after Nondisjunction
Cell Division
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Cell Division
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Trisomy 21 Karyotype
Normal Human Karyotype
Cell Division
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Trisomy 21
Cell Division
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