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Aim: Why is meiosis important?

Aim: Why is meiosis important?. Do Now: Label each phase of cell division (IPMATC). So, what is the difference between mitosis and meiosis ?. Mi t osis 2 identically diploid cells (same as parent ) Makes cells used for growth, repair, development & asexual development. Meiosis

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Aim: Why is meiosis important?

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  1. Aim:Why is meiosis important? • Do Now: Label each phase of cell division (IPMATC)

  2. So, what is the difference between mitosis and meiosis?

  3. Mitosis • 2identically diploid cells (same as parent) • Makes cells used for growth, repair, development & asexual development • Meiosis • 4 genetically different haploid cells • Makes cells for Sexual reproduction • Genetic info is exchanged/rearranged.

  4. Meiosis I Contains all phases of mitosis Homologous chromosomes separated I PMATC I Pray More At The Church

  5. Interphase I • This is where the chromosomes are duplicated, replicated, or copied.

  6. Eukaryotic Cell Cycle

  7. Prophase I • Chromosomes condense. The nuclear envelope breaks down. “Crossing Over” occurs.

  8. “Crossing Over”-Chromatids exchange genetic material

  9. Metaphase I • Pairs of homologous chromosomes move to the cell’s middle. Metaphase = Move Middle

  10. Anaphase I • Homologous chromosomes move to the cell’s opposite poles.

  11. Telophase I • Chromosomes gather at the poles. • The cytoplasm divides.

  12. What about cytokinesis? • In cytokinesis, the nuclear membrane is reforming around each new cell. • Cytokinesis happens after the division of chromosomes and cells are made.

  13. Meiosis II NO INTERPHASE and NO REPLICATION of chromosomes!! PMAT

  14. Prophase II • A new spindle forms around the chromosomes.

  15. Metaphase II • Chromosomes line up at the middle.

  16. Anaphase II • Centromeres divide, and chromatids move to opposite poles.

  17. Telophase II • A nuclear envelope forms around each set of chromosomes. The cells divide.

  18. What do we end up with at the end of meiosis? • 4 haploid cells

  19. Answer to Aim:Why is meiosis important? • Allows genetic information from 2 parents to combine to form offspring that are different from both parents.

  20. Aim: Why is genetic variation so important? Do Now: Copy the chart on the side board. Fill in the blank areas about Mitosis and Meiosis.

  21. Mitosis vs Meiosis

  22. What is a homologous chromosome? Chromosomes that have the same sequence of genes, that have the same structure, and that pair during meiosis.

  23. Chromatid is a single strand of chromosomes. Chromosomes are 2 chromatids together, made of condensed chromatin. Centromereis where the two chromatids meet.

  24. Chromatinare ribbon-liked structures of DNA and histone proteins.

  25. Label the chromosome

  26. “Crossing Over”-Chromatids exchange genetic material (Occurs during Prophase I in Meiosis.)

  27. Why is crossing over important? • With out it, every one will look the same! • New combinations of genetics • Variety Crossing Over Video

  28. Crossing over is one of the several processes that lead to genetic variation. • The rearranging of genetic info leads to genetic variation in offspring.

  29. Genetic Variability • Natural Selection • Allows for adaptation and ultimate survival of certain organisms when the environment changes.

  30. 3 Ways to Promote Genetic Variation • 1. Crossing over • 2. Independent Assortment • 3. Random Union of sperm and egg

  31. Tetrad-a pair of homologous chromosomes. As the tetrads form, the chromosomes exchange parts of their chromatids during the process of crossing over.

  32. Disjunction Tetrads separate equally as a result of a process known as disjunction. During what phase does this occur? Anaphase

  33. Non-disjunction Tetrads separate UNEQUALLY. • Uneven # of chromosomes will result in the gametes. If these gametes are fertilized, the offspring will have either 1 too many chromosomes or 1 too few chromosomes. Example of Result of non-disjunction: Down’s Syndrome

  34. Down’s Syndrome • The non-disjunction of the 21st chromosome. • Occurrence: One in every 700 American children.

  35. Answer to Aim:So why is genetic variability so important???

  36. Allele Different forms of the same gene. • For example, humans have genes for eye color. However, there exists an allele for brown eyes and an allele for blue eyes. Responsible for Dominant or Recessive Traits

  37. Each individual has 2 allele’s, one on each chromatid. • You can have 2 of the same alleles or 2 different alleles. • The dominant allele will determine what trait you have.

  38. Dominant Traits: The traits that come out in the individual. * Only 1 dominant trait is needed. Expressed as the capital letter. • Recessive Traits: The “weaker” trait that we do not see unless there are 2 of them. Expressed as the lower case letter. AA, Aa, aA aa

  39. What color eyes does each individual have?

  40. Activity in text page 253 on crossing over.

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