1 / 32

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
Download Presentation

Unit 2- Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related