Do Now

1. Do Now • Humans have 46 chromosomes (or 23 pairs of chromosomes). We just learned how mitosis works. • How many chromosomes do the daughter cells of mitosis have? • In sexual reproduction, each parent’s cells contribute their chromosomes to the offspring. How can this occur? • What would happen if for three generations each parent gave a full set of their chromosomes to their offspring? How many chromosomes would that 3rd generation have?

2. In your notes, number your paper 1-10. Look at the photo and write down which phase each one is showing.

3. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Chapter 10 Meiosis Video

4. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Terms • Somatic Cells: Body Cells. Contain two sets of chromosomes (23 pairs = 46 chromosomes) • Gametes: Sex Cells (necessary for sexual reproduction). Contain 1 set of chromosomes (23 chromosomes). • Diploid: (2n): Contains two sets of chromosomes. • Haploid: (n): Contains one set of chromosomes. • Fertilization: is the union of sperm and egg • The zygote has a diploid chromosome number, one set from each parent

5. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Homologous Chromosomes • Somatic cellshave pairs of homologouschromosomes, receiving one member of each pair from each parent • Homologous chromosomes are matched in • Length • Centromere position • Gene locations • A locus (plural, loci) is the position of a gene • Different versions of a gene (alleles) may be found at the same locus on maternal and paternalchromosomes

6. Do Now 1/23/14 • Haploid cells of a southern gray tree frog are 1n = 12. What is the diploid number? • Describe in your own terms what a locus is.

7. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Chromosomes are matched in homologous pairs • The human sex chromosomes X and Y differ in size and genetic composition • Pairs of autosomes have the samesize and genetic composition • Applying Your Knowledge • If there is one pair of sex chromosomes, how many pairs of autosomes are found in humans?

8. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? 0 Homologous pair of chromosomes Centromere One duplicated chromosome Sister chromatids

9. 0 Haploid gametes (n = 23) n Egg cell n Sperm cell Meiosis Fertilization Diploid zygote (2n = 46) 2n Multicellular diploid adults (2n = 46) Mitosis and development

10. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? 0 Meiosis reduces the chromosome number from diploid to haploid • Like mitosis, meiosis is preceded by interphase • Chromosomes duplicate during the S phase • Unlike mitosis, meiosis has two divisions • During meiosis I, homologous chromosomes separate • The chromosome number is reduced by half • During meiosis II, sister chromatids separate • The chromosome number remains the same, however the copies have separated.

11. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Meiosis • Almost all human cells contain 23 pairs of chromosomes, or a full set equaling 46 total. • Called body, or somatic cells. • All somatic cells are said to be diploid (2n), meaning having twosetsof chromosomes.

12. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Meiosis • In order for sexual reproduction to take place, there must be a means for both parents to contribute their chromosomes. • For this reason, sex cells, or gametes are produced with only one set of chromosomes, or 23 total chromosomes. • Gametesare said to be haploid (n) meaning they only have one set of chromosomes. • Haploid gametes are produced by a process known as meiosis.

13. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Meiosis • Meiosis: A process of cell division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell (2n) into four haploid (n) daughter cells. • Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

14. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Homologous Pairs • We speak about humans having 23 pairs of chromosomes. • Those pairs are called homologous pairs. • Each pair comes from a different parent. • Chromosomes are named from 1 to 22, X & Y based on size. • Each parent will pass on one set of their 23 chromosomes to the offspring.

15. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Homologous Pairs • 22 of the homologous pairs are exactly alike in size, location of the centromere, and the banding sequence viewed when staining. • The X & Y, or sex chromosomes, are dissimilar in size, and appearance.

17. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? 2n Father 2n Mother Meiosis Meiosis 1n Father Gamete 1n Mother Gamete New 2n Organism Fertilization

18. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Meiosis Stages • Meiosis usually involves 2 distinct stages • Meiosis I • Meiosis II

19. Meiosis Video

20. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Prophase I • Chromosomes coil & condense. • Each chromosome pairs with its corresponding homologous chromosome by synapsis, to form a tetrad. • There are 4 sister chromatids, 2 per replicated chromosome, in a tetrad. • Crossing-over may occur here • Crossing-over is when chromosomes overlap and exchange portions of their chromatids.

23. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Metaphase I • Tetrads align at the center of equator • Spindle fibers attach to the chromosomes

24. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Anaphase I • The fibers pull the homologous chromosomes toward opposite ends of the cell.

25. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Telophase I & Cytokinesis • Duplicated chromosomes have reached the poles • A nuclear envelope forms around chromosomes • Each nucleus has the haploid number of chromosomes • The cell separates into 2 cells. • After telophase I and cytokinesis • How many chromosomes are present in one human cell? • How many chromatids are present in one human cell?

26. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Telophase I

27. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Telophase I vs. Telophase

28. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Meiosis I Results • Meiosis I results in two haploid (N) cells. • Each cell has half the number of chromosomes as the original cell. • Lost one copy of each homologous pair. Remaining copy still has sister chromatid attached at the centromere.

29. Do Now 1/24/2014 • What are homologous pairs? • What are sister chromatids? • Why is meiosis important? • Based on what you already know, how is meiosis different than mitosis?

30. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? 0 MEIOSIS I: Homologous chromosomes separate METAPHASE I PROPHASE I ANAPHASE I INTERPHASE Centrosomes (with centriole pairs) Microtubules attached to kinetochore Sister chromatids remain attached Metaphase plate Sites of crossing over Spindle Tetrad Nuclear envelope Centromere (with kinetochore) Sister chromatids Homologous chromosomes separate Chromatin

31. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Meiosis II • The haploid cells will then go through a second round of cellular division. • The sister chromatids will move to the center of the cell. • The centromeres split, separating the sister chromatids. • The individual chromosomes are then pulled to the opposite poles, where daughter nuclei form. • Cells pinch off, left with four haploid daughter cellseach containing one set of chromosomes (n).

32. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? 0 MEIOSIS II: Sister chromatids separate TELOPHASE I & CYTOKINESIS TELOPHASE II AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS PROPHASE I METAPHASE II ANAPHASE II Cleavage furrow Haploid daughter cells forming Sister chromatids separate

33. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Gamete Formation • In males, meiosis results in 4 sperm cells • In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.

35. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter3/animation__how_meiosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter3/animation__how_meiosis_works.html

36. Without using your books or notebooks, give as many similarities and differences between the processes of Mitosis and Meiosis. • You may work with your partner.

37. 1 (s-phase) 1 (s-phase) 1 2 2 4 Diploid (2n) Haploid (n) Homologous Pairs forming tetrads Sister Chromatids Identical Variation Somatic Cells Gametes

38. EQ: What is Meiosis? Why is meiosis important? How is meiosis different from mitosis? Mitosis vs Meiosis

39. EQ: How does meiosis increase genetic variation? Essential Question • How does meiosis increase genetic variation?

40. EQ: How does meiosis increase genetic variation? Genetic Variation • Independentorientationof chromosomes in meiosis and randomfertilizationlead to varied offspring Animation

41. EQ: How does meiosis increase genetic variation? Independent Orientation of Chromosomes • Independent orientation at metaphase I • Each pair of chromosomes independently aligns at the cell equator • There is an equal probability of the maternal or paternal chromosome facing a given pole • The number of combinations for chromosomes packaged into gametes is 2nwhere n = haploid number of chromosomes

42. EQ: How does meiosis increase genetic variation? What did I just learn? • Why are you not identical (unless you’re an identical twin) to your siblings, or anyone else?

43. EQ: How does meiosis increase genetic variation? Why you are unique: • Based on independent orientation at metaphase I, the number of different eggs (and sperm) for humans is 223 = about 8 million.

44. EQ: How does meiosis increase genetic variation? Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring • Random fertilization • The combination of each unique sperm with each unique egg increases genetic variability • So with the union of unique gametes, the probability of two siblings having exactly the same genetic profile is 1 out of 64 trillion possibilities.

45. Homologous chromosomes can carry different versions of genes • Separation of homologous chromosomes during meiosis can lead to genetic differences between gametes • Homologous chromosomes may have different versions of a gene at the same locus • We call different forms of the same genes alleles. • One version was inherited from the maternal parent, and the other came from the paternal parent • Since homologues move to oppositepoles during anaphase I, gametes will receive either the maternalorpaternalversionof the gene

46. EQ: How does meiosis increase genetic variation? 0 Brown coat (C); black eyes (E) White coat (c); pink eyes (e)

47. EQ: How does meiosis increase genetic variation? 0 Coat-color genes Eye-color genes C E Brown Black C E C E Meiosis c e e c c e White Pink Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes

48. 0 Crossing over further increases genetic variability EQ: How does meiosis increase genetic variation? • Genetic recombination is the production of new combinations of genes due to crossing over • Crossing over involves exchange of genetic materialbetween homologous chromosomes • Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and crossing over • Corresponding amounts of genetic material are exchanged between maternal and paternal (nonsister) chromatids Animation: Crossing Over

49. EQ: How does meiosis increase genetic variation? 0 Tetrad Chiasma Centromere

50. Coat-color genes Eye-color genes 0 C E Tetrad (homologous pair of chromosomes in synapsis) c e Breakage of homologous chromatids 1 C E c e Joining of homologous chromatids 2 C E Chiasma c e Separation of homologous chromosomes at anaphase I 3 C E C e c E c e Separation of chromatids at anaphase II and completion of meiosis 4 C E Parental type of chromosome C e Recombinant chromosome E c Recombinant chromosome e c Parental type of chromosome Gametes of four genetic types