1. Meiosis

2. Quick Review of MITOSIS

3. What happens to the DNA BEFORE mitosis? DNA synthesis (replication) Why? Needs an exact copy for the new “daughter cells”

4. 2 types of cells: Somatic Cell = body cell – Example: skin, muscle, lung cells – Diploid cells Gamete = sex cell – Example: egg, sperm, pollen – Haploid cells

5. Haploid Cells vs. Diploid Cells Haploid = have 1 of EACH kind of chromosome (n) Diploid = have 2 of EACH kind of chromosome (2n)

6. Meiosis = cell division that produces ½ the chromosomes of the parent cell; makes gametes

7. What does meiosis produce? SEX CELLS (aka: gametes, haploid cells)

8. Why do we need Meiosis?

9. How is MITOSIS different from MEIOSIS?

10. Meiosis Vocabulary Homologous Chromosome = 2 pairs of sister chromatids (form a tetrad); same order and letter of gene

11. How do we get diploid cells? Mitosis!

12. How do we get haploid cells? MEIOSIS!

15. Will Meiosis or Mitosis occur in these cells? Skin cells Pollen Ovum/ovules Muscle cells

16. What is genetic variation? Genetic variation = the differences between genes of individuals of a species or populations of different species. Which two individuals will have the least genetic variation in their genes? A.Brother and sister B.Brother and cousin C.Sister and cousin D.Mother and nephew

17. Which two species will have the greatest genetic variation between species. 1.Lancelet and Lamprey 2. Lancelet and Leopard 3. Salamander and Leopard 4. Turtle and Leopard

18. Meiosis provides genetic variation among organisms 2 sources of genetic variation: 1.Random alignment of chromosomes during metaphase 2.Crossing Over

19. Chromosome alignment can vary!

20. Crossing Over = exchange of genetic information during prophase I of meiosis – Provides MORE variation – Basis for evolution – This is a form of genetic recombination (or the recombining of genes!)

21. Chromosome Action Explains Mendel’s Work Law of segregation – Traits are separately inherited from parents Law of independent assortment – Traits are inherited independently of each other Rule of dominance – If its dominant it will appear; recessive will only appear if there is a “double dose”

22. http://www.sumanasinc.com/webcontent/ani mations/content/meiosis.html http://www.sumanasinc.com/webcontent/ani mations/content/meiosis.html

23. QUIZ TIME! What are some examples of gametes? Egg Sperm

24. Haploid or Diploid? Sex cells Somatic cells Body cells Sperm Egg

25. QUIZ TIME! How can you tell if a homologous chromosome will be homologous?

26. Mitosis or Meiosis? Gametes produced Diploid cells produced Haploid cells produced Half the number of chromosomes produced Same number of chromosomes produced

27. QUIZ TIME! During what phase of meiosis does crossing over occur?

28. QUIZ TIME! If a cell starts with 20 chromosomes how many chromosomes will be present in the cells following meiosis? How many chromosomes would be present following mitosis in the same original cell?

29. QUIZ TIME! How many cells are produced during mitosis? 1  2 How many cells are produced during meiosis? 1  4

30. Mistakes in Meiosis

31. What do the chromosomes have to do in meiosis in order for it to be successful? One chromosomes from each homologous pair moves to each pole of the cell…

32. What if the chromosomes fail to separate? Nondisjunction = the failure of homologous chromosomes to separate properly during meiosis

33. What does nondisjunction do to the chromosome count? One cell has too many chromosomes Another cell has too few chromosomes

34. When would you notice the effects of nondisjunction? Seen after gametes fuse  fertilization When a gamete with an extra chromosome is fertilized by a normal gamete, the zygote will have an extra chromosome… It should have 2, but has three! This is called trisomy

35. What if an organism is lacking chromosomes? Organisms with an extra will often survive BUT organisms lacking one or more, usually do not survive

36. When a gamete with a missing chromosome fuses with a gamete with normal chromosome number, you get monosomy

37. What if BOTH gametes have extra sets of chromosomes? Produces offspring with 4 sets of chromosomes This is called a tetraploid Organisms with more than the usual number of chromosomes are called polyploids

39. Polyploids in plants Very useful commercially – Tetraploid wheat (4n) – Triploid apples (3n) Plant breeders use chemicals to artificially cause nondisjunction to get these polyploid plants. Why could this be an area of concern for humans?