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Cell Division: The Miracle of Life Explained

Delve into the intricate world of cell division, from mitosis to meiosis. Unravel the mystery of zygotes, chromosomes, and the cell cycle. Witness the magic of creating new life through the process of genetic recombination and independent assortment. Learn about the stages of mitosis and meiosis and understand the significance of genetic variation. Explore the fascinating world of cell reproduction and discover the secrets hidden within every nucleus.

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Cell Division: The Miracle of Life Explained

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  1. Ch. 8 Cell Reproduction • What is cell division? • Mitosis • What is a zygote? • It forms when the male and female gametes unite. • All cells come from preexisting cells • DNA is inside a rod-shaped structure called a? • Chromosomes

  2. Chromosomes • Every chromosome consists of two identical parts called sister chromatids. Each half is a chromatid. • The point where each chromatid crosses or attaches to the other chromatid is called the centromere. • Chromatids only occur during S phase of interphase. • Every cell has a certain # of chromosomes in the cell. (Pg. 146) • Ex. Humans=46, chicken=78, cat=32, chimp=48, dog=78 • Pg. 145  Histones are proteins that DNA wraps around in eukaryotic cells.

  3. Why do all organisms have an even # of chromosomes? • Chromosomes are in pairs called homologous chromosomes. • A diploid (2N) cell has both chromosomes that make up the homologous pair. • A haploid (1N) cell has only 1 half of the homologous pair. • Sex chromosomes determine the sex of the offspring (X or Y). • Autosomes are all the chromosomes except the sex chromosomes. We have 44 or 22 pair. • Karyotype – a map of the chromosomes.

  4. Cell Cycle • 3 parts to the cell cycle • 1. Interphase – resting & growth stage (3 parts – G1, S, & G2) • 2. Mitosis – cell division (4 parts) • 3. Cytokinesis- produces 2 daughter cells • Pg. 149 • There are approximately 100 trillion cells in an average human. • Some cells divide every 20 to 30 minutes in a animal embryo.

  5. 4 Stages of Mitosis • Prophase – 1st stage of mitosis • Chromosomes start to coil and shorten. • Centrioles form and migrate to each end. • Animals only have centrioles from the centrosomes. Pg. 150 • Spindle fibers form between the two centrioles. • Nuclear membrane & nucleolus break down and disappear.

  6. Metaphase • 2nd phase of mitosis • The chromosomes are attached to the spindle fibers. • The spindle fibers arrange the chromosomes in a line at the middle of the cell.

  7. Anaphase • 3rd stage in mitosis • The centromeres are pulled apart as the spindle fiber shortens and separates the sister chromatids in half. • Now each chromatid is at opposite ends.

  8. Telophase • 4th phase of mitosis • The chromatins reach the opposite poles of the cell. • The spindle fiber & centrioles disappear • The chromatids uncoil • The nucleolus reappears and a new nuclear envelope forms around each set of chromosomes.

  9. Cytokinesis • The plasma membrane pinches off and 2 new identical cells are formed. • The 2 new cells are called daughter cells.

  10. Interphase(1st part of the cell cycle) • Resting and growth stage • The chromatins are duplicated in order to form a sister chromatin, which is two identical chromatins. • The cell is preparing to undergo mitosis. • Mitosis Video

  11. Meiosis • Reduction of Division  Meiosis • Meiosis I produces 2 daughter cells, each with half the homologous chromosome. Go from one cell with 46 chromosomes (2N) to two daughter cells with 23 (1N) chromosomes. Draw. Pg. 154-155 • Meiosis II occurs after meiosis I. The 2 daughter cells divide to produce 4 haploid cells. • These haploid cells are gamete cell, either egg cells or sperm cells. • Meiosis Video

  12. Differences in Meiosis vs. Mitosis • 1. Form synapsis in prophase – homologous chromosomes pair up. • Each pair of homologous chromosomes is called a tetrad. • 2. Crossing-over occurs when the chromatids twist and reattach to the opposite homologous chromosome in the tetrad. Pg. 154. • 3. The outcome of Meiosis I is 2 new cells with half the number of chromosomes as the original cell, but the 2 new cells have two copies of the chromosomes because of replication before Meiosis I. • Meiosis II does not have replication, so the final product is 2 new cells (4 total now) with half the chromosomes (haploid – 1N).

  13. Genetic recombination is the result of crossing-over during prophase/metaphase of Meiosis I. This causes a mixing of genetic material. • Independent assortment – is the random separation of chromosomes during prophase/metaphase of Meiosis I. This causes genetic variation of maternal and paternal chromosomes. • Cell Division Video • Mitosis vs. Meiosis

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