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Meiosis

Meiosis. Lesson Objectives. Minds ON Learning Goals Yesterday’s Recap What is Meiosis Homework. Minds ON. Budding in Humans? http:// www.youtube.com/watch?v=NADx1ot0uhI. Learning Goals .

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Meiosis

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  1. Meiosis

  2. Lesson Objectives • Minds ON • Learning Goals • Yesterday’s Recap • What is Meiosis • Homework

  3. Minds ON Budding in Humans? http://www.youtube.com/watch?v=NADx1ot0uhI

  4. Learning Goals • Investigate the process of meiosis, using a microscope or similar instrument, or a computer simulation and draw biological diagrams to help explain the main phases in the process (D2.2) • Explain the phases in the process of meiosis in terms of cell division, the movement of chromosomes, and crossing over of genetic material (D3.1) • Use appropriate terminology related to genetic processes: haploid, diploid, spindle (D2.1)

  5. Yesterday’s Recap Mitosis: • Occurs when a parent cell divides to produce two daughter cells • Hereditary information stays the same during each division • Chromosomes are made of DNA and other proteins, which are folded and condensed into chromosomes • Cell cycle: Interphase (growth and replication of DNA), prophase, metaphase, anaphase and telophase , cytokinesis

  6. Yesterday's Recap Continued… Di=2 Diploid Number: (2n) number of each chromosome in a body cell of an organism; having two chromosomes of each type per cell Haploid Number: (n) number of chromosomes in a cell that contains a single set of chromosomes (gametes or sex cells); one-half the diploid number Ha = half ½ Full complement; Humans: 2n = 46 (not actually distintive units Number of unique chromosomes; Humans: n=23 Therefore, the number of homologous pairs is 23

  7. Haploid/Diploid • In a humans, there are 22 pairs of autosomes (non-sex cells) and 1 pair of sex chromosomes (XX=female; XY=male) = 23 pairs in total • Haploid numbered chromosomes usually occur in gametes or sex cells (sperm/eggs) • Diploid numbered chromosomes usually occur in body cells (tissue cells, etc.)

  8. Meiosis • Mitosis occurs in body cells and creates IDENTICAL daughter cells • Meiosis occurs in reproductive tissues where sperms and eggs are formed. It ensures VARIATION and ensures that the zygote has the correct number of chromosomes. • Variation occurs in two ways: Independent (Random) Assortment and Crossing Over.

  9. Mitosis and Meiosis in Life Source: http://www.mysearch.org.uk/website1/html/433.Cycles.html

  10. Independent (Random) Assortment • When chromosomes line up side-by-side (tetrad) during Metaphase I, the paternal and maternal chromosomes line up randomly on the left and right • = 8 388 608 different combinations!

  11. So let’s try it… • I need 4 males and 4 females to stand up and line up facing each other. • Is there more than one possible way to do this? MMMM FMFM MMFF FFMM F FFF MFMF FFMM MMFF

  12. Crossing Over • While the dyads (X-shaped chromosomes) are in a tetrad (lined up side-by-side), pieces of homologous chromatids can change places creating different chromosomes. Note: If one piece gets misplaced, a genetic mutation will occur (genes are missing or misplaced).

  13. So let’s try it… • I need 4 males and 4 females to stand up and line up facing each other. • Take your genetic information (your cards) that match your real characteristics and trade each other (make sure they are homologous traits). • What has happened? Explain.

  14. Stages of MeiosisThere are two stages in Meiosis: Meiosis 1 and Meiosis II Meiosis I • Homologous chromosomes come together in synapsis (crossing over can occur here) • Main difference from mitosis is that genetic sharing occurs; the rest of the function afterwards is similar to Mitosis • Chromosomes are diploid at the beginning, become haploid by telophase I Meiosis II • Sister chromatids line up again, then separate • During telophase II, four haploid cells result • Four haploid cells result by the end of telophase II.

  15. Meiosis – what it looks like http://www.youtube.com/watch?v=D1_-mQS_FZ0

  16. Homework • Sheets • Meiosis sheets • Text book work (sheet from yesterday) • Lesson questions

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