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Cellular Division copyright cmassengale

Cell Division All cells come from pre-existing cells Differs in prokaryotes and eukaryotes. In eukaryotes, new cells are produced for growth or to replace damaged/old cells that no longer work right. copyright cmassengale

Identical Daughter Cells
Two identical daughter cells Parent Cell copyright cmassengale

Keeping Cells Identical
DNA contains the instructions for making cells work correctly and together. It is important that each new cell contain a complete, duplicated set of DNA to avoid problems. copyright cmassengale

Two new, identical DNA strands
DNA Replication DNA Replication copies the DNA so each new cell will then have an identical copy of the DNA. While mistakes may happen, they are usually minor and the new cell will work fine. Big mistakes cause the cell’s death or malfunction. Original DNA strand Two new, identical DNA strands copyright cmassengale

Chromosomes copyright cmassengale

Prokaryotic Chromosome
The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane. This one chromosome requires very little work to be copied and placed into a new cell. copyright cmassengale

Eukaryotic Chromosomes
Each chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be seen when cells aren’t dividing and are called chromatin copyright cmassengale

Eukaryotic Chromosomes
All eukaryotic cells store genetic information in chromosomes Most eukaryotes have between 10 and 50 chromosomes in their body cells. If they reproduce sexually, they are set in pairs since they get one from each parent (male and female). Human body cells have chromosomes (23 pair) copyright cmassengale

Chromosomes in Dividing Cells
Duplicated chromosomes are called chromatids & are held together by the centromere One of the sister chromatids you received from your mom and the other from your dad. Called Sister Chromatids copyright cmassengale

Karyotype A Karyotype is a picture of the chromosomes from a human cell arranged in pairs by size First 22 pairs are called autosomes Last pair are the sex chromosomes XX = female XY = male copyright cmassengale

The Y Chromosome Decides
Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome copyright cmassengale

Cell Division in Prokaryotes
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Cell Division in Prokaryotes
Prokaryotes, like bacteria, divide into 2 identical cells by binary fission Single chromosome makes a copy of itself Cell wall forms between the chromosomes dividing the cell Parent cell Chromosome replicates Cell splits 2 identical daughter cells copyright cmassengale

Prokaryotic Cell Undergoing Binary Fission

Animation of Binary Fission

The Cell Cycle copyright cmassengale

Phases of the Cell Cycle
Interphase G1 - primary growth phase S - synthesis; DNA replicated G2 - secondary growth phase Mitosis (M phase) Prophase Metaphase Anaphase Telophase Cytokinesis (C phase)

Interphase - G1 Stage 1st growth stage after cell division
Cells mature by making more cytoplasm & organelles Cell carries on its normal activities *Cells are preparing themselves to be big enough to divide.

Two identical copies of DNA
Interphase – S Stage Synthesis stage DNA is copied or replicated Two identical copies of DNA Original DNA

Interphase – G2 Stage 2nd Growth Stage
Occurs after DNA has been copied All cell structures needed for division are made (e.g. centrioles) Both organelles & proteins are synthesized

What’s Happening in Interphase?
What the cell looks like Animal Cell What’s occurring

Mitosis

Mitosis Division of the nucleus Only occurs in eukaryotes
Has four stages Doesn’t occur in some cells such as brain cells Varying lengths of depend on different cells

Four Mitotic Stages Prophase Metaphase Anaphase Telophase copyright cmassengale

Prophase Chromatids in the nucleus condense and become chromosomes that are clearly visible Nuclear membrane & nucleolus are broken down Spindle fibers (kinetochores) form between poles attach to centromere of each chromosome pair

Sketch The Spindle

Spindle Fiber attached to Chromosome

What the cell looks like
Review of Prophase What the cell looks like

Metaphase Chromosomes, attached to the spindle fibers, move to the center of the cell Chromosomes are now lined up at the equator Pole of the Cell Equator of Cell

Metaphase Asters at the poles Spindle Fibers Chromosomes lined at the Equator copyright cmassengale

Review of Metaphase What the cell looks like

Anaphase Occurs rapidly
Sister chromatids are pulled apart to opposite poles of the cell by spindle fibers

Anaphase Review What the cell looks like What’s occurring

Telophase Sister chromatids at opposite poles
Spindle fibers disassembles Nuclear envelope reappears and forms nucleus around each set of sister chromatids (two nuclei) Nucleolus reappears Cytokinesis begins and the cell starts to be formed into two new cells Chromosomes reappear as chromatin

Comparison of Anaphase & Telophase

Cytokinesis Means division of the cytoplasm
In plants, a cell plate forms at the center of the cell In animals, a cleavage furrow pinches the cell in half Division of cell into two, identical halves called daughter cells Cleavage furrow Cell plate

Mitotic Stages

Daughter Cells of Mitosis
Have the same number of chromosomes as each other and as the parent cell from which they were formed Identical to each other, but smaller than parent cell Must grow in size to become mature cells (G1 of Interphase)

Identical Daughter Cells
What is the 2n or diploid number? Chromosome number the same, but cells are smaller than parent

Review of Mitosis copyright cmassengale

Draw & Learn these Stages

Name the Mitotic Stages:
Interphase Name this? Prophase Telophase Name this? Metaphase Anaphase copyright cmassengale

Eukaryotic Cell Division
Used for growth and repair Produce two new cells identical to the original cell Cells are diploid (2n) Chromosomes during Metaphase of mitosis Cytokinesis Anaphase Prophase Metaphase Telophase copyright cmassengale

Name each stage as you see it occur?
Mitosis Animation Name each stage as you see it occur? copyright cmassengale

Mitosis in Onion Root Tips
Do you see any stages of mitosis? copyright cmassengale

Test Yourself over Mitosis

Mitosis Quiz copyright cmassengale

Name the Stages of Mitosis:
Early prophase Early Anaphase Metaphase Interphase Early Telophase, Begin cytokinesis Late Prophase Late telophase, Advanced cytokinesis Mid-Prophase Late Anaphase copyright cmassengale

Early, Middle, & Late Prophase Telophase & Cytokinesis
Identify the Stages ? Early, Middle, & Late Prophase ? ? ? Metaphase Anaphase Late Prophase ? ? ? Telophase & Cytokinesis Late Anaphase Telophase copyright cmassengale

Locate the Four Mitotic Stages in Plants
Anaphase Telophase Metaphase Prophase copyright cmassengale

Uncontrolled Mitosis If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell Cancer cells copyright cmassengale

Meiosis Formation of Gametes (Eggs & Sperm)

Facts About Meiosis Preceded by interphase which includes chromosome replication Two meiotic divisions --- Meiosis I and Meiosis II Called Reduction- division Original cell is diploid (2n) Four daughter cells produced that are monoploid (1n) copyright cmassengale

Facts About Meiosis Daughter cells contain half the number of chromosomes as the original cell Produces gametes (eggs & sperm) Occurs in the testes in males (Spermatogenesis) Occurs in the ovaries in females (Oogenesis) copyright cmassengale

More Meiosis Facts Start with 46 double stranded chromosomes (2n) After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) Occurs in our germ cells that produce gametes copyright cmassengale

Why Do we Need Meiosis? It is the fundamental basis of sexual reproduction Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote copyright cmassengale

Fertilization – “Putting it all together”

Replication of Chromosomes
Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere Occurs in Interphase Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere. copyright cmassengale

A Replicated Chromosome
Gene X Sister Chromatids (same genes, same alleles) Homologs (same genes, different alleles) Homologs separate in meiosis I and therefore different alleles separate. copyright cmassengale

Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by half Fertilization then restores the 2n number from mom from dad child too much! meiosis reduces genetic content The right number! copyright cmassengale

Meiosis: Two Part Cell Division
Sister chromatids separate Meiosis I Meiosis II Homologs separate Diploid Diploid Haploid copyright cmassengale

Meiosis I: Reduction Division
Nucleus Spindle fibers Nuclear envelope Early Prophase I (Chromosome number doubled) Late Prophase I Metaphase I Anaphase I Telophase I (diploid) copyright cmassengale

Prophase I Late prophase Chromosomes condense. Spindle forms. Nuclear envelope fragments. Early prophase Homologs pair. Crossing over occurs. copyright cmassengale

Tetrads Form in Prophase I
Homologous chromosomes (each with sister chromatids) Join to form a TETRAD Called Synapsis copyright cmassengale

Crossing-Over Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Produces Genetic recombination in the offspring copyright cmassengale

Homologous Chromosomes During Crossing-Over

Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment copyright cmassengale

Homologous pairs of chromosomes align along the equator of the cell
Metaphase I Homologous pairs of chromosomes align along the equator of the cell copyright cmassengale

Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres. copyright cmassengale

Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale

Meiosis II Only one homolog of each chromosome is present in the cell. Gene X Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Sister chromatids carry identical genetic information. copyright cmassengale

Meiosis II: Reducing Chromosome Number
Prophase II Metaphase II Telophase II 4 Genetically Different haploid cells Anaphase II copyright cmassengale

Prophase II Nuclear envelope fragments. Spindle forms. copyright cmassengale

Metaphase II Chromosomes align along equator of cell. copyright cmassengale

Anaphase II Equator Pole Sister chromatids separate and move to opposite poles. copyright cmassengale

Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale

Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome copyright cmassengale

Meiosis Animation copyright cmassengale

Oogenesis or Spermatogenesis
Gametogenesis Oogenesis or Spermatogenesis copyright cmassengale

Spermatogenesis Occurs in the testes Two divisions produce 4 spermatids Spermatids mature into sperm Men produce about 250,000,000 sperm per day copyright cmassengale

Spermatogenesis in the Testes
Spermatid copyright cmassengale

Spermatogenesis copyright cmassengale

Oogenesis Occurs in the ovaries Two divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasm Immature egg called oocyte Starting at puberty, one oocyte matures into an ovum (egg) every 28 days copyright cmassengale

Oogenesis in the Ovaries

Oogenesis Oogonium (diploid) Mitosis Primary oocyte Meiosis I Secondary (haploid) Meiosis II (if fertilization occurs) First polar body may divide Polar bodies die Ovum (egg) Second polar body a A X Mature egg copyright cmassengale

Comparing Mitosis and Meiosis

Comparison of Divisions
Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction copyright cmassengale

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