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Bell Ringer
Cell Division Review
Units 5 & 6
Prokaryotic Cell Division
• Prokaryotic Cell Division = Binary Fission
• After DNA replication occurs, the cytoplasm divides. There is NO nucleus, so mitosis does NOT happen.
This process is called
Binary Fission
DNA
Replication
Cytokinesis
This is the Cell Cycle
M Phase
Eukaryotic Somatic (Body) Cell Division =
Mitosis Stages of Cell Cycle
• Interphase – G1 = Growth – S = DNA replication – G2 = Prepare for Mitosis
• M Phase – Mitosis = Division of Nucleus
• Prophase • Metaphase • Anaphase • Telophase
– Cytokinesis = Division of Cytoplasm
MITOSIS
REPRODUCTION OF BODY CELLS
PRODUCES
2 IDENTICAL DIPLOID CELLS
Interphase • Cell Grows
& Prepares for Division
• DNA is Replicated
Prophase • Chromosomes
become visible
• Nuclear Membrane & Nucleolus Disappear
• SPINDLE FORMS
EARLY LATE
Metaphase • Spindle Fibers
attach to the Centromeres
• Chromosomes Line up in the Middle/ Equator
Anaphase
• Sister Chromatids are Pulled Apart (separated) to opposite poles of the cell
Telophase • Nuclear
Membrane & Nucleolus Reform
• Chromosomes Unwind into Chromatin
Cytokinesis • Cytoplasm Divides
• 2 Identical daughter cells form with the SAME number of chromosomes as parent cell
Occurs during Telophase
MITOSIS
END RESULT:
Produces 2 Genetically Identical
Diploid Body (Somatic) Cells
Cytokinesis • ANIMAL CELL • PLANT CELL
MEIOSIS
REPRODUCTION OF SEX CELLS
PRODUCES
4 GENETICALLY DIFFERENT HAPLOID GAMETES
Interphase • Cell Grows
& Prepares for Division
• DNA is Replicated
Meiosis I
Prophase I Metaphase I Anaphase I Telophase I
Meiosis II
Prophase II Metaphase II Anaphase II Telophase II
2 Stages of
Division
HAPLOID 4
Crossing Over Synapsis/Tetrad = Homologous Chromosomes
Pair Up & Cross Over • Crossing Over begins during Prophase I & ends during Anaphase I
• Crossing Over is important because
– It increases Genetic Diversity
– It ensures that all cells produced during meiosis are Different
– It Unlinks genes
Homologous Chromosomes
Pair Up & Cross Over
Homologous Chromosomes
Line Up In The Middle
(double line)
Meiosis I
Homologous Chromosomes
Separate
Chromosomes Line Up
in the Middle
(single line)
Sister Chromatids
Separate
Spindle Reforms &
Chromosomes Attach
Meiosis II
Produces 4 Genetically Different
Haploid Gametes (Sex Cells)
1 ovum (egg) produced
4 sperm produced
Fertilization
Zygote
Karyotype: Male or Female?
Karyotype: Male or Female?
Human Gametes normally have 23 chromosomes.
Human Body Cells normally have 46 chromosomes
(23 pairs).
What is this disorder called? Down’s Syndrome OR Trisomy 21
This is caused by Nondisjunction.
Nondisjunction can occur during Anaphase I OR Anaphase II of
meiosis if the chromosomes do not SEPARATE correctly.
Stage of Meiosis =
Anaphase I
Stage of Meiosis =
Anaphase II
Too Many
Chromosomes
Chromosomes
Line Up in the
Middle/Equator
Homologous
Chromosomes
Line Up in the
Middle/Equator
Crossing
Over
Sister Chromatids Separate
Homologous
Chromosomes
Separate
Haploid
Diploid
2
Identical
Body Cells
4
Genetically Different Gametes
(sex cells)