Notes on Chromosomes, Mitosis, & Meiosis

1. Notes on Chromosomes, Mitosis, & Meiosis

2. What is a chromosome? • Chromosomes = condensed DNA, same material, coiled more tightly into individual bundles • Chromatin = DNA that is uncoiled, unorganized, not individually visible • DNA is a large polymer composed of sugars, phosphates, & ‘bases’.

5. 1 arm of a chromosome Chromosomes 400x Chromatin wrapped >> around histone proteins DNA molecule Chromatin w/o histone proteins

10. History of discovery • First seen and named “colored bodies” by Flemming in 1882 • Similarity to Mendel’s factors noted by Sutton in 1902

11. Identifying chromosomes • number of chromosomes varies in different species • # of chromosomes does not correlate with anything • 46 chromosomes in humans (23 pairs) • Each chromosome pair is named by a number, except…

12. Types of chromosomes • ”Sex” chromosomes discovered by Morgan in 1908 • called ‘X’ and ‘Y’ chromosomes because of different shapes • In humans and most animals • XX = female, XY = male

13. Types of chromosomes • All the other chromosomes are called Autosomes, • These are known by number only

14. Cell Divsion

15. A cell spends most of its life growing and maintaining its molecules and organelles. Cells that divide must double their contents during this growth period, or they would become progressively smaller over several divisions and eventually lose key components. This growth period is called interphase, and it lasts from 10 hours to an animal’s lifetime, depending upon the type of cell.

16. Because DNA is the hereditary material, its duplication is a critical interphase activity for potentially dividing cells. In early interphase, called the G1 (“Gap 1”) phase of the cell cycle, no DNA is made in most cells.Then suddenly, as if on cue, DNA synthesis begins at several sites on each chromosome and continues for several hours, stopping when a copy of each chromosome has been made. This period of DNA synthesis is known as S phase, and although highly variable, it typically lasts about 8-10 hours.

17. Following the S phase, there is another gap period, the G2 Phase (yellow), in which proteins that have a role in cell division are produced. Some of these proteins cause the chromosomes to condense into compact units, while others are involved in the breakdown of the nuclear membrane.

18. The M phase (red) of the cell cycle consists of two processes; mitosis, or nuclear division, followed by cytokinesis, or cytoplasmic division. These processes occur in animals as they develop from fertilized eggs and as they replace worn out tissues.

19. Replication of chromosomes • Replication of DNA = exact and complete duplication of original strand • Replication proceeds at a replication fork along both ‘halves’ of the original • Complementary strands are known as parent and daughter strands

20. Replication of DNA

21. Mitosis • Reproduction of a somatic cell is an exact duplication of the original • ie. The daughter cells are exact clones • They have the same # of chromosomes • This # (different for each species) is known as the diploidnumber of chromosomes • Somatic cells must be distinguished from sex cells , found only in testes or ovaries

22. Mitosis is a special kind of cell division used by eukaryote cells. You will find a series of diagrams in your text & notes which shows the stages of mitosis; these are:* prophase* metaphase* anaphase* telophase Mitosis is really a division of the nucleus into two identical nuclei. It is followed by cytokinesis which is the division of the cytoplasm into two.

24. Phases of Mitosis interphase interphase telophase prophase anaphase metaphase

25. Prophase Metaphase Anaphase Telophase

27. Late Telophase

28. A cell spends most of its life growing and maintaining its molecules and organelles. Cells that divide must double their contents during this growth period, or they would become progressively smaller over several divisions and eventually lose key components. This growth period is called interphase, and it lasts from 10 hours to an animal’s lifetime, depending upon the type of cell.

29. Interphase with symbols for chromosomes

30. Prophase with symbols for chromosomes

31. ‘Prometaphase’ with symbols for chromosomes

32. Metaphase with symbols for chromosomes

33. Anaphase with symbols for chromosomes

34. Telophase with symbols for chromosomes

35. Cytokinesis with symbols for chromosomes

36. Mitosis

38. Mitosis Animation

39. Mitosis animation U Ariz site: http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/mitosis_movie.html Mitosis animation Cells Alive site: http://www.cellsalive.com/mitosis.htm Mitosis-Meiosis Activity: http://biologyinmotion.com/cell_division/ Excellent Kean Univ Video of Overall Cell Cycle & Mitosis: http://www.kean.edu/~fglazer/PPT/ANIMS/lw04_cell_cycle_final.swf Kean Univ Video on Meiosis: http://www.kean.edu/~fglazer/PPT/ANIMS/lw13_meiosis.swf

41. Chromosomal Replication Paired chromatids

42. Meiosis • Meiosis is the reproduction of sex cells (as opposed to somatic cells) • This process occurs only in the testes or ovaries • New cells (known as gametes) have only half the number of chromosomes of the parent cells • This # (different for each species) is known as the haploidnumber of chromosomes

43. Mitosis

44. Meiosis I

45. Meiosis II

46. Meiosis Animation with crossing-over

48. Prophase 1 & Crossing over

49. Second phase of meiosis, yielding haploid gametes at bottom

50. Meiosis 1