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November 12 th , 2013

November 12 th , 2013. Leave out your section 6.2 PN & vocab to be stamped. Seatwork instructions: Do you think it’s ethical to bring a species back from extinction? Write 2-3 sentences explaining your position. You must support your claim using at least one piece of information from the video.

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November 12 th , 2013

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  1. November 12th, 2013 • Leave out your section 6.2 PN & vocab to be stamped. • Seatwork instructions: Do you think it’s ethical to bring a species back from extinction? Write 2-3 sentences explaining your position. You must support your claim using at least one piece of information from the video.

  2. Agenda • Nov. 12: Meiosis & crossing over • Nov. 14: Mendelian genetics • Nov. 19: Mendelian genetics cont. • Nov. 21: Incomplete dominance & codominance • Nov. 26: Chapter 5-7 test: Cell division & genetics

  3. Mitosis

  4. Mitosis

  5. Learning Target • LT: • Students will be able to describe the process of mitosis. • SC: • I will be able to describe the similarities and differences between the processes of mitosis and meiosis.

  6. Meiosis • Mitosis focuses on the replication of somatic cells. • Somatic cells make up most of your tissues and organs. • Ex. Eyeballs, kidney, spleen • Meiosis focuses on the replication of gametes. • Gametes are sex cells which are used in sexual reproduction. • Ex. Ova (eggs) and spermatozoa (sperm)

  7. Haploid & Diploid • Somatic cells and gametes have different numbers of chromosomes. • Somatic cells are diploids (2n), meaning that they have two sets of chromosomes. • Gamete cells are haploids (1n), meaning that they have one set of chromosomes.

  8. Haploid & Diploid • Analogy of a pair of gloves: • If you had 23 pairs of gloves, you would have a total of 46 gloves. • Each pair has an identical partner.

  9. Homologous Chromosomes • Similarly, your somatic cells have 23 pairs of chromosomes, for a total of 46. • “Paired” chromosomes are called homologous chromosomes.

  10. Homologous Chromosomes • Chromosome pairs 1 through 22 are autosomes. • Autosomes contain genes that are not directly related to the sex of an organism. • The 23rd pair contains sex chromosomes that directly control the development of sexual characteristics. • In humans, we say that an organism with two X chromosomes is female (XX), and with one X and one Y is male (XY).

  11. Meiosis • Meiosis is a form of nuclear division that divides a diploid cell (2n) into a haploid cell (1n). • It is essential for sexual reproduction– or the fusion of two gametes – to occur. • During fertilization, you inherit one copy of chromosomes from your mother’s egg (1n), and one copy of chromosomes from your father’s sperm (1n). • Sexual reproduction allows for genetic variability. • Without it, we would all be clones of our parents.

  12. Fertilization 1n Ovum 1n Sperm Haploid 2n Zygote Diploid

  13. Asexual Reproduction • Not all organisms utilize sexual reproduction. • Some organisms utilize asexual reproduction, which results in offspring that are genetically identical to the parent. • Prokaryotes and some eukaryotes reproduce asexually. • These organisms do not undergo meiosis.

  14. Homologous chromosomes • Homologous chromosomes are similar – but not identical to each other. • They are the same length & carry the same genes. • You inherited one homologous chromosome from your father and one from your mother. • Sister chromosomes are duplicated, identical copies of a chromosome that are attached by the centromere.

  15. Meiosis • A cell undergoing meiosis divides twice: • In Meiosis I, homologous chromosomes separate. • In Meiosis II, sister chromatids separate. • Result is four haploid cells.

  16. Meiosis I • Prophase I: • Cell prepares for division (nuclear membrane breaks down; centrioles & spindle fibers move and assemble). • Homologous chromosomes begin to condense and pair up. • Crossing over occurs.

  17. Crossing Over • Crossing over is the exchange of chromosome segments between homologous chromosomes.

  18. Crossing Over • Crossing over results in a new combination of genes. • It is a form of recombination, which is the mixing of any parental genes. • It increases genetic diversity by creating new, varied gene combinations on a chromosome. • It is responsible for siblings looking similar, but not identical to each other.

  19. Meiosis I • Metaphase I: • Spindle fibers align the homologous chromosomes along the cell equator. • Each side of the equator has chromosomes from both parents.

  20. Meiosis I • Anaphase I: • The paired homologous chromosomes separate from each other and move toward opposite sides of the cell. • Sister chromatids remain attached.

  21. Meiosis I • Telophase I: • The spindle fibers disassemble. • Nuclear membrane re-forms. • Cell undergoes cytokinesis. • Resulting cells have 23 duplicated chromosomes (sister chromatids).

  22. Meiosis II • Prophase II: • Centrosomes and centrioles move to opposite sides of the cell. • Spindle fibers begin to assemble.

  23. Meiosis II • Metaphase II: • Spindle fibers align the chromosomes (still attached as sister chromatids) along the cell equator.

  24. Meiosis II • Anaphase II: • Sister chromatids are pulled apart from each other and move to opposite sides of the cell.

  25. Meiosis II • Telophase II: • The nuclear membrane re-forms around the chromosomes. • Spindle fibers break down. • Cell undergoes cytokinesis.

  26. Gametogenesis • Meiosis results in haploid cells. • These cells are incapable of fertilization until gametogenesis occurs. • Male gametes undergo spermatogenesis and female gametes undergo oogenesis.

  27. Spermatogenesis • Spermatogenesis produces four, small male gametes, known as spermatozoa.

  28. Oogenesis • Oogenesis produces one ovum (egg) and two polar bodies. • The ovum receives most of the organelles, cytoplasm, and nutrients during cytokinesis. • The polar bodies have little more than DNA inside them and are eventually broken down.

  29. Errors in Meiosis • In very rare occasions, an error will occur during meiosis in which one of the resulting gametes has one too many chromosomes, and another has one too few. • Some of these gametes can still be fertilized and produce viable offspring.

  30. Trisomy • The result of this fertilization is trisomy. • Individuals with trisomy have 47 chromosomes instead of 46. • Commonly known genetic disorders include: • Trisomy 21 (Down syndrome) • Trisomy 18 (Edwards syndrome) • 47,XXX (Triple X syndrome) • 47,XXY (Klinefelter syndrome) • 47,XYY

  31. Trisomy • Resultant offspring have a specific set of symptoms that is dependent on the type of genetic disorder. • Trisomy 21: • Physical growth delays, a particular set of facial characteristics, & severe degree of intellectual disability. • 47,XXY: • Delayed development, less muscle mass, less facial and body hair, larger breasts, & broader hips. • 47,XXX: • The only genetic condition that usually results in no distinguishable difference between normal population.

  32. Venn Diagram • Create a venn diagram describing the similarities and differences between mitosis and meiosis.

  33. Homework • Section 6.6: • Vocab • PowerNotes • Reinforcement • Snurfle meiosis • Watch video: http://bit.ly/Snurfle • Complete worksheet

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