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Heredity Concept 1: Meiosis

Heredity Concept 1: Meiosis. Agenda for 10/28/2013. Wake up work #1 Get new packets! Concept 1 Notes p. 2-5 Draw the steps of Meiosis 1 and Meiosis II. Wake Up Work #1. What are the stages of Cell Division/Mitosis? I______________ P_____________ M_____________ A_____________

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Heredity Concept 1: Meiosis

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  1. HeredityConcept 1: Meiosis

  2. Agenda for 10/28/2013 • Wake up work #1 • Get new packets! • Concept 1 Notes p. 2-5 • Draw the steps of Meiosis 1 and Meiosis II

  3. Wake Up Work #1 • What are the stages of Cell Division/Mitosis? • I______________ • P_____________ • M_____________ • A_____________ • T_____________ • C_____________ • What is the end result of Mitosis (cytokinesis)?

  4. Let’s think Back to Mitosis: Recall learning about mitosis during the Cells Unit: • Cell Cycle: G1, S, G2(interphase) and P,M,A,T (mitosis) • DNA was replicated during S stage • Cell divided during Mitosis– produced 2 identical cells • Mitosis is used for growth and repair, to make more identical cells • Cells made during mitosis are called diploid– meaning they have 2 copies of every chromosome (one from mom, one from dad) • In humans, diploid cells have 46 chromosomes (23 pairs) • We call these somatic cells or body cells

  5. Another type of cell division: • Organisms that reproduce sexually (like humans) combine genetic information from two parents to produce offspring. • What would happen if you combined two diploid cells? 46 + 46 = 92 chromosomes! Uh oh- that’s not a human!! Do you want your child to be an aquatic rat?

  6. Which brings us to…the whole purpose of Meiosis • We would like our offspring to be the same species as us! How do we do that? • Each parent only passes on HALF of their chromosomes (23) – one from each pair – so the offspring ends up with a full set (46). • Meiosis is the process of creating gametes – sex cells that have HALF the normal number of chromosomes. We call these cells haploid because they only have one of each chromosome. • These cells are used ONLY for sexual reproduction (sperm in males or eggs in females).

  7. Major Types of Cells • TWO major types of cells in your body: • Somatic cells (body cells) make up most of your body tissues and organs. *Diploid, 2n* • Divides by Mitosis • Skin Cells, blood cells, muscle cells, nerve cells, etc. • Gametes  sex cells that have half the number of chromosomes as somatic cells *Haploid, n* • Divide by Meiosis • Ova – eggsfrom the female • Spermatozoa – spermcells from the male

  8. Your Cells have Two Types of Chromosomes: • Autosomes – chromosome pairs 1 through 22 • They contain genes that code for most of the proteins your body needs • Males and females have exactly the same chromosomes for pairs 1-22. • Sex chromosomes – determines the gender of the individual • Humans inherit 2 sex chromosomes, X and Y. (one from mom and one from dad) • XX is female • XY is male • This is the 23rd pair of chromosomes.

  9. Is this a female or a male?

  10. Remember: Chromosomes • Each species has a specific number of chromosomes per cell—chromosomes are tightly coiled up DNA in a rod-like shape • Humans have 46 chromosomes, which come in 23 pairs

  11. Homologous Chromosomes • One chromosome from mom and one chromosome from dad • A pair that contains the same genes, for example they could both contain hair color and eye color • They have the same length and general appearance

  12. Diploid and Haploid Cells • During sexual reproduction, the # of chromosomes is important! • Diploid –two full sets of chromosomes • Somatic/body cells • “2n” • For humans, n=23, so 2*n=46 chromosomes in body cells! • Haploid –one full set of chromosomes • Gametes/sex cells • “n” • For humans, n=23, so 23 chromosomes in sex cells!

  13. Sexual Reproduction • Sexual reproduction  Organisms that reproduce sexually (like humans) combine genetic information from two parents to produce offspring • Fertilization—the actual fusion of an egg and sperm cell to form a zygote Each parent only passes on HALF of their chromosomes (23) – one from each pair – so the offspring ends up with a full set (46).

  14. Process of Meiosis

  15. Overview • Purpose: to make sex cells (egg and sperm) • Form of cell division that divides a diploid cell into haploid cells (half the amount of chromosomes) • Meiosis occurs in 2 steps: Meiosis I: Reduction from haploid to diploid Meiosis II : Separation of sister chromatids. Haploid daughter cells from Meiosis I divide. Results in four haploid daughter cells called gametes, or sex cells (egg and sperm) with undoubled chromosomes

  16. MEIOSIS I

  17. Meiosis I • Meiosis I begins with interphase, in which cells: • Increase in size • Make proteins • Replicate DNA

  18. Prophase I Nuclear membrane breaks down Centrioles separate and make spindle fibers Homologous chromosomes pair up Exchange of genetic material between pairs occurs in a process called crossing over.

  19. Crossing Over • Sometimes chromosomes can cross over each other and get “tangled” when they pair up in Prophase I. • When this happens, they swap pieces of DNA ,(a piece from the maternal chromosomes switches places with a piece on the paternal chromosome). • This process creates new combinations of genes – chromosomes that are “part mom/ part dad.”

  20. Metaphase I Homologous Chromosomes line up in the middle of the cell in pairs (double row).

  21. Anaphase I The chromosome pairs separate. Homologous chromosomes move to opposite ends of the cell. Sister chromatids remain attached.

  22. Telophase I (and Cytokenesis) Chromosomes gather at the poles Nuclear membrane forms & the cytoplasm divides (this is called cytokinesis) End result:2 daughter cells that have a unique combination of 23 duplicated chromosomes from both parents

  23. MEIOSIS II

  24. Prophase II The nuclear membrane breaks down. Spindle fibers form in each of the daughter cells & attach to the centromeres of the sister chromatids.

  25. Metaphase II Chromosomes line up across the middle of the cell (equator)

  26. Anaphase II The sister chromatids are pulled apart from each other & move to opposite sides of the cell.

  27. Telophase II(and Cytokenesis) Nuclear membrane forms in each cell and cytoplasm divides End Result: Four, genetically unique, haploid daughter cells. Each contains one set of chromosomes

  28. II

  29. Wake Up Work #2 • What is the outcome of Meiosis 1? • What is the outcome of Meiosis II? • Include how many chromosomes it has in reference to the parent cell. • The purpose of meiosis is to make ___________ in females and _____________ in males. • What takes place during Prophase I that causes genetic variation to occur? • What is fertilization?

  30. Agenda 3/27 • Finish up assignment from yesterday • Mitosis versus Meiosis • Pages 6,9,10 • Review for Quiz tomorrow

  31. COMPARING MITOSIS AND MEIOSIS

  32. Mitosis and Meiosis

  33. Mitosis and Meiosis

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