MEIOSIS Chapter 11-4

1. MEIOSIS Chapter 11-4

2. Warm Up Chapter11-4 • What does diploid mean? • What does haploid mean? • How many chromosomes does mitosis produce in a cell? • How many chromosomes does meiosis produce in a cell? • What are homologous chromosomes?

3. Warm Up Chapter 10 and 11-4 • How many chromosomes do humans have? • What does Meiosis do so that each cell does not have 92 chromosomes during fertilization? • Mitosis produces what kind of cells? • Meiosis produces what kind of cells? • How many cells does Mitosis produce? • How many cells does Meiosis produce?

4. Meiosis cuts down the number of chromosomes in our cells to 23, so they can come together and create a cell with 46 chromosomes • -Meiosis creates variance - 23 chromosomes from mom, 23 chromosomes from dad • - Creates variants through reproduction

5. 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). a. This is a good idea if you’re going to combine two cells to make a new organism. B. This trick is accomplished by halving chromosome number.

6. 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. a. This makes for a lot of genetic diversity. This trick is accomplished through and crossing-over. b. Genetic diversity is important for the evolution of populations and species.

7. The purpose of MITOSIS is to produce twoIDENTICAL(diploid) cells. The purpose of MEIOSIS is to produce fourASSORTED and DIFFERENT(haploid)cells.

8. Mieosis vs. Mitosis Animation 1:00 Mitosis/Meiosis Quiz Meiosis/Mitosis side by side PPT Dr. Thinkwell. Meiosis I and II 5:15

9. Cornell Notes… • Meiosis and Mitosis • Mitosis goes through PMAT once. • Meiosis goes through PMAT twice. • Prophase I • Metaphase I • Anaphase I • Telophase I • Cytokinesis • Prophase II • Metaphase II • Anaphase II • Telophase II • Cytokinesis MEIOSIS I MEIOSIS II

10. Cornell Notes… MEIOSIS I

12. Mieosis vs. Mitosis Animation 1:00 Mitosis/Meiosis Quiz Meiosis/Mitosis side by side PPT Dr. Thinkwell. Meiosis I and II 5:15 Thinkwell.Spermatogenesis 2.3

13. Concept Check 10 and 11 – Fill out the chart (What are the differences)

14. Cornell Notes… • Meiosis and Mitosis • During Prophase I, Meiosis undergoes “Crossing Over” between the paired chromatids. • Mitosis has NO crossing over. • Prophase I has crossing over between the chromatids resulting in the chromosomes of the offspring being DIFFERENT than either parent.

15. Cornell Notes…

16. Crossing-Over

17. The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis The first (and distinguishing) division of meiosis Mitosis

20. End P6

21. The process of Meiosis • 2 Parts to Meiosis… Meiosis I and Meiosis II • Meiosis I is very similar to Mitosis • Interphase I – same as mitosis – the cell is growing – DNA replicates tetrads (4 sets of chromosomes) • Prophase I – chromosome pair together to make homologous pairs • Metaphase I – tetrads(4) stack and form in the middle (crossing over occurs) allows for more diversity • Anaphase I – homologous chromosome go to each side – they don’t separate they form dyads (2) • 5. Telophase I – nuclear membranes form – cytokinesis

23. Meiosis II – going straight from Telophase I 6. Prophase II – diploid cells now – (2n) – each cell has same amount as the parent cell 7. Metaphase II – similar to mitosis – line up in the middle (centromeres on midline) 8. Anaphase II – chromosomes separate 9. Telophase II – nucleus forms and cytokinesis results in 4 haploid cells (n).

26. End P5 P7

27. Understanding Chromosomes • Somatic Cells ( Normal Human Body cells) • = 46 chromosomes (23 sets) • Diploid = 2 n • 2. Gametes (sex cells – sperm and egg) = 23 Chromosomes with one set • Haploid – 1n - not paired • 3. Ploidy – the number of chromosomes in a single cell. • some diseases happen when there is a different # • (Down’s syndrome has 47 chromosomes) • Down’s syndrome has 3 chromosomes for chromosome #21.

28. Keys to Understanding Meiosis 1. Chromosomes are paired. 2. Chromosomes carry genes. 3. The gene forms on a pair of chromosomes may be homologous or non-homologous

29. Crossing-Over

30. Spermatogenesis Men are busy – meiosis produces roughly 250,000,000 sperm per day.

31. Oogenesis – Women are less busy in meiosis than men – meiosis produces only a few hundred mature eggs over a lifetime.

32. What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction.

33. End P3

34. We are all unique – 1 chromosome from mom and one from dad we are half like our parents, which are half like their parents, which are half like their parents and so on … That creates diversity! – We are 1/2 our parents, 1/4 like our grandparents, 1/8 of our great grandparents  go back so many years – that’s how different we all are from each other.

35. Meiosis I – Prior to Meiosis I, each chromosome is replicated to form a tetrad = X X Name ________ Date_________ Phase Metaphase I Spinal fibers attach to entire chromosome Phase Prophase I Each chromosome pairs with its corresponding chromosomes “homologous” to form a tetrad. \ Phase Crossing Over Exchange portions of chromatids

36. Between Independent Assortment and Crossing-Over, No Two Gametes Are Identical.

37. Y chromosome X chromosome Boy or Girl? The Y Chromosome “Decides”

38. Boy or Girl? The Y Chromosome “Decides”

39. “Putting It All Together” - Fertilization

40. One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes. In humans, n = 23 and 223≈ 8,000,0000. That’s a lot of diversity by this mechanism alone.

42. Crossing over Meiosis Following a Single Chromosome Pair