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Do Now:. What is Mitosis? What are the phases of mitosis? How many chromosomes are in a human body (somatic) cell?. Sexual reproduction. How is sexual reproduction different from asexual reproduction?. Sexual Reproduction. Transfer of genetic material from one organism to another

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  1. Do Now: What is Mitosis? What are the phases of mitosis? How many chromosomes are in a human body (somatic) cell?

  2. Sexual reproduction • How is sexual reproduction different from asexual reproduction?

  3. Sexual Reproduction • Transfer of genetic material from one organism to another • Gametes: special sex cells • One male, one female • Fertilization: fusion of the nuclei of male and female gametes • Zygote: single cell formed from fusion

  4. Vocab • Somatic cells: body cells (in humans they have 46 chromosomes) • Homologous chromosomes: chromosomes that are grouped together to make up a pair (23 pairs in human somatic cells)

  5. Meiosis • Special kind of cell division that forms gametes • Gametes have half the number of chromosomes as the parent cell.

  6. Vocab continued… • Diploid: 2n • Characteristic of cells that have ALL homologous chromosomes • Ex. Somatic cells • Haploid: n • cells that have only one chromosome from each pair (monoploid) • Ex. Gametes, spores (plants)

  7. Meiosis: reduction division • Each cell divides TWICE. • Chromosomes replicate only ONCE. • Takes place in special cells • Cells start out with diploid number of chromosomes. • Each original cell produces four daughter cells, each with the haploid number of chromosomes.

  8. Stages similar to mitosis • Each of the two divisions show a prophase, metaphase, anaphase, and telophase stage similar to mitosis.

  9. Order of stages • Prophase I • Metaphase I • Anaphase I • Telophase I • Prophase II • Metaphase II • Anaphase II • Telophase II

  10. Prophase I • Each pair of chromatids line up with homologous pair and become fastened at centromeres. • Synapsis: pairing of homologous pairs • Tetrad: each group of 4 chromatids • Crossing-over: exchange of segments between chromatids during synapsis • Nuclear membrane disappears • Spindle fibers form

  11. Metaphase I • Centromeres of tetrads line up on the equator • Tetrads fastened to spindle microtubules at centromeres

  12. Anaphase I • Disjunction: separation of homologous chromosomes of each tetrad • Cluster of chromosomes around each pole is haploid (BUT each chromosome is double stranded)

  13. Telophase I • End of 1st meiotic division • Cytoplasm divides • 2 daughter cells with half the number of parent cell’s chromosomes, but with each chromosome in replicated form • Cell is ready for next division • Exactly like mitosis

  14. Prophase II • Each of the daughter cells forms spindle and double-stranded chromosomes move toward middle of spindle

  15. Metaphase II • Chromosomes fastened to spindle microtubules at centromeres • Centromeres line up on the equator • Chromosomes still have 2 strands or chromatids

  16. Anaphase II • Centromeres divide • 2 chromatids separate, each becoming a single-stranded chromosome • 2 chromosomes move toward opposite ends of spindle

  17. Telophase II • Both daughter cells divide forming 4 haploid cells. • In each cell, chromosomes return to interphase state, and nuclear membrane forms again.

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