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
MITOSISREPRODUCTION 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
MEIOSISREPRODUCTION 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 21This 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
HaploidDiploid
2Identical Body Cells
4
Genetically Different Gametes (sex cells)
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