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Unit 2- Genetics

Unit 2- Genetics. Meiosis. Sperm _____ chromosomes. Fertilization. Egg ____ chromosomes. X. Zygote 46 chromosomes. Which is diploid ? Which is haploid ?. 23 chromosomes. Sex cells. Egg 23 chromosomes. How can a diploid cell become haploid cells Answer: by the process of meiosis

jillian-erickson
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Unit 2- Genetics

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  1. Unit 2- Genetics Meiosis

  2. Sperm _____ chromosomes Fertilization Egg ____ chromosomes X Zygote 46 chromosomes Which is diploid ? Which is haploid ?

  3. 23 chromosomes Sex cells Egg 23 chromosomes How can a diploid cell become haploid cells Answer: by the process of meiosis Meiosis: process of cell division in which a diploid cell produces four haploid daughter cells; each with half the number of chromosomes found in the parent cell

  4. Recall where DNA is within the cell

  5. Interphase • DNA replicates/duplicates (S phase) • In the form of chromatin • Not easily visible • Similar to interphase in Mitosis

  6. Before any cell division, DNA must be duplicated • Were going to use a simpler cell in which 2n=4 • This cell have 4 unduplicated chromosomes right before meiosis occurs

  7. Thus, this cell has 2 pairs of homologous chromosomes • We are now ready for meiosis with Playdoh

  8. What you need • 3 different colored playdoh • One color for paternal chromosome • One color for maternal chromosome • One color for centromere • Paper or surface of whiteboard • Pen/marker to draw other details such as cell membrane, spindle fibers, centrioles etc. • Handout • Group of 3

  9. 2 parts of meiosis • Meiosis 1: reduction division • Meiosis 2: Gametes are produced • Unlike mitosis, meiosis does not occur in somatic cells of our body but rather in reproductive organs.

  10. Prophase 1 Tetrad: the homologous pair made of 4 chromatids. • Chiasmata: region where crossing-over occurs.

  11. Tetrad: the homologous pair made of 4 chromatids. • Chiasmata: region where crossing-over occurs.

  12. Prophase 1 • Chromosomes condense and become visible; each with 2 identical sister chromatids. • Nuclear membrane dissolves; centrioles move to opposite cell poles; spindle fibers form • Homologous chromosomes pair up and form a tetrad • Crossing-over occuring between homologous chromosomes produce exchange genetic information

  13. Your cell should look like this now

  14. Metaphase 1 • Homologous chromosomes line up in PAIRS in the middle of the cell • Again: Homologous chromosomes do not line up in a single file; they line up in pairs in metaphase 1

  15. Anaphase 1 • Homologous chromosomes (NOT individual sister chromatids) separate and move to opposite end of cell.

  16. Telophase 1 • Two haploid cells (half of the original amount in each cell that is, 2 each) • Original cell (2n= 4 chromosomes) • Homologues reach opposite sides of the cell. • A nuclear membrane reforms forming 2 new nuclei • Chromosomes relax

  17. Meiosis 2: similar to mitosisProphase 2 • Chromatin coil again • Spindle fibers attach to chromosomes • THERE IS NO DUPLICATION OF CHROMOSOME AT THIS STEP • No Crossing over either

  18. Metaphase 2 • Chromosomes line up in single file RANDOMLY in the middle of each cell

  19. Anaphase 2 • Centromeres split pulling sister chromatids to opposite end of each cell

  20. Telophase 2 • Four nuclei form around chromosomes • Spindle fibers dissolve • Cells divide

  21. Final result of meiosis Initial parent cell 2n=4 4 haploid daughter cells n = 2

  22. RECAP MEIOSIS https://www.youtube.com/watch?v=vA8aMpHwYh0

  23. Gametogenesis= the formation of gametes involves Spermatogenesis in male and oogenesis in female

  24. No DNA duplication occur here

  25. Chromosome Crossing over • Only one chiasma is illustrated but many occur per pair (Plural: chiasmata)

  26. 22 = 4 possible combinations to forms a gamete

  27. Some new words • Gamete: a sex cell; includes sperm cells and egg cells • Zygote: a cell produced by the fusion of two gametes • Fertilization: the formation of a zygote by fusing two gametes • Haploid: a cell containing half the usual number of chromosomes (n) • Diploid: a cell containing two copies of each chromosome (2n)

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