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Understanding Meiosis: The Process and Its Significance in Genetic Variation

This lesson provides an in-depth look at meiosis, the process that produces gametes with half the genetic information of parent cells. It highlights the importance of meiosis in sexual reproduction and genetic variation. The two main stages of meiosis (Meiosis I and II) are explored, including key phases such as Prophase I where crossing over occurs, leading to genetic recombination. Understanding meiosis is crucial for comprehending how offspring can have varied traits through natural selection. Prepare to share insights about your learning on this vital biological process.

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Understanding Meiosis: The Process and Its Significance in Genetic Variation

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Presentation Transcript

  1. Warm Up • Locate your notes on mutations • Be prepared to share what you learned about mutations with the class.

  2. Meiosis Part I Monday; March 19, 2012

  3. Essential Questions • How can mitosis and meiosis each contribute to the production of offspring with varying traits? • How can sexual reproduction (meiosis) result in a great variety of possible gene combinations and contribute to natural selection?

  4. What is Meiosis? • Meiosis – Produces gametes containing half the number of chromosomes as the parent cell • Occurs only in the sex organs • Gametes – male (sperm) and female (egg) sex cells produced by specialized body organs • Humans: • Body Cell – 46 chromosomes • Sex Cell (Gamete) – 23 chromosomes

  5. Importance of Meiosis • Without Meiosis, all offspring resulting from fertilization would have twice the amount of genetic information as its parents. • If too much genetic information is present within the nucleus, it can have adverse effects on the offspring.

  6. Importance of Meiosis • Meiosis solves this issue by producing gametes with half the amount of genetic information as the parent. • Allows for sexual reproduction and therefore, genetic variation

  7. Crossing Over • Crossing over – when genetic material is exchanged due to the tight pairing of homologous chromosomes • Occurs during Prophase I (in Meiosis I) • 2 – 3 crossovers per pair of chromosomes • Results in new combinations of alleles and genetic variation • Allele – alternative forms of a gene, and therefore a trait

  8. Meiosis • Consist of two separate divisions • Meiosis I • Starts with 1 Diploid (2n) cell and results in 2 Diploid (2n) cells • Meiosis II • Starts with 2 Diploid (2n) cells and results in 4 Haploid (n) cells • Males = 4 Haploid sperm cells • Females = 1 Hapoid egg cell and 3 haploid polar bodies

  9. Phases of Meiosis I 1. Interphase 2. Meiosis I A. Prophase I (Crossing over occurs) B. Metaphase I C. Anaphase I D. Telophase I

  10. Interphase • Begins with a single 2n parent cell that is located in the sex organ • DNA is replicated resulting in a cell with 4 times the amount of chromosomes (4n) • After replication, two identical sister chromatids are present

  11. Prophase I • Chromosomes and spindle fibers are present • Homologous chromosomes come together, matched gene by gene, to form a tetrad. • Tetrad – consist of two homologous chromosomes paired tightly together • Homologous chromosomes – paired chromosomes with genes for same traits arranged in the same order

  12. Metaphase I • Centromeres of each chromosome become attached to a spindle fiber • Spindle fiber pulls the tetrad into the middle of the nucleus • Homologous chromosomes are lined up side by side as tetrads

  13. Anaphase II • Homologous chromosomes separate and move to opposite ends of the cell • Centromeres holding the sister chromatidsdo not split • Each new cell receives only one chromosome from each homologous pair

  14. Telophase I • Spindle fibers beak down • Chromosomes uncoil • Cytoplasm divides to yield two new cells • Resulting cells only have half the genetic information of original cell from each homologous pair

  15. Meiosis I • Beginning of Meiosis I • 1 Diploid (2n) Parent cell, located in the sex organ, was present • End of Meiosis I • 2 Diploid (2n) Daughter cells, located in the sex organ, is present • These 2 Diploid Daughter Cell will divide again during Meiosis II • Meiosis Video

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