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)