1. Chromosomes 3.2 Mr. McGee, IB Biology (HL)

2. By the End, You Will Understand: Prokaryotes have one chromosome consisting of circular DNA. Some prokaryotes also have plasmids, but rarely eukaryotes. Eukaryote chromosomes are linear DNA with histone proteins. In a eukaryote species, there are different chromosomes which contain different genes. Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes. Diploid nuclei have pairs of homologous chromosomes. Haploid nuclei have one chromosome pair. The number of chromosomes is a characteristic of a species. A karyotype shows the chromosomes of an organism in homologous pairs of decreasing length. Sex is determined by sex chromosomes; autosomes are extras.

3. By the End, You Will Have the Following Applications and Skills: Cairns’ technique for measuring the length of DNA molecules by autoradiography. Comparison of genome size T2 phage, E. coli, D. melanogaster, H. sapiens & P. japonica. Comparison of diploid chromosomes numbers in H. sapiens, P. troglodytes, C. familiaris, O. sativa & P. equorum. Use of karyotypes to deduce sex and diagnose different disorders. Use of databases to identify the locus of a human gene and its polypeptide product.

4. Theory of Knowledge (TOK) In 1922 the total number of chromosomes counted in a human cell was 48. This remained the established number for 30 years, even though a review of photographs from the time clearly shows that there were only 46. For what reason(s) do existing beliefs carry a certain inertia?

5. Chromosome Basics

6. What is a Chromosome? Chromosomes are organized and packaged DNA. Prokaryotes only have ONE circular coil of DNA. – There are no free ends (this would make replication more complex). There is usually no associated proteins. It is very simple. Eukaryotes usually have many chromosomes which are separate strands of DNA. – There are free ends to the DNA; proteins are combined with the DNA to aid in folding. It can appear as an “I” or an “X,” depending on if it has duplicated itself.

7. Plasmids: Extra Genetic Information Plasmids are very small circular coils of DNA. They are present in prokaryotes but rarely in eukaryotes. They can self-replicate. Plasmids are extra pieces of genetic information that can actually transfer back and forth from nearby bacteria, providing a mechanism for genetic recombination (just like sex). Plasmids are not necessary but rather aid the bacteria. – They are in a sense a flash drive; they carry additional information and allow it to transfer.

8. Eukaryotic Chromosomes

9. Eukaryotic Chromosomes are linear; they are straight, non- coiled and have two free ends. All free segments of DNA wind-up around histones (proteins) to allow coiling up of the chromatin into chromosomes.

10. The chromosomes in a person’s cell nucleus.

11. You get one chromosome from mom and one chromosome from your dad. A pair of identical chromosomes are called homologous chromosomes. – A human has 23 pairs of homologous chromosomes. – A human thus has 46 total chromosomes.

12. Chromosomes replicate their other side, giving them an “X” appearance. 1 2 3

13. Karyotypes -A chart showing all pairs of an organisms chromosomes laid out

15. What is a karyotype? A chart that shows all of the chromosomes in an organism is called a karyotype. Autosomes are chromosomes #1-22. – They contain genes for the body. Sex chromosomes are the 23 rd pair. – They determine gender. – Girls have an XX. Boys have an XY.

17. Boy or Girl? Examine the sex chromosomes: XX XY = Girl = Boy Which is the boy? Which is the girl?

18. It’s a boy

19. Quiz (Half Sheet of Paper) 1.What is the difference between chromosomes and DNA? 2.Where in the cell is DNA found? 3.How many pairs of chromosomes do humans have? 4.If sex chromosomes are an XX, what is the gender? 5.What are autosomes?

20. Homologous Chromosomes

21. I thought that chromosomes were shaped like an “X”?

22. Why are Chromosomes Shaped Like an “X”? Because chromosomes replicate their other half. Sometimes, they are shown as an “I”, and others as an “X”. ?

23. 1.Boy or Girl? 2.What’s wrong with this karyotype?

24. Turner Syndrome (Monosomy X)

27. 1.Boy or Girl? 2.What’s wrong with this karyotype?

28. Down Syndrome (Trisomy 21)

29. 1.Boy or Girl? 2.What’s wrong with this karyotype?

30. Cri-du-Chat Syndrome (5p Deletion)

31. 1.Boy or Girl? 2.What’s wrong with this karyotype?

32. Klinefelter Syndrome (XXY)

33. 1.Boy or Girl? 2.What’s wrong with this karyotype? Nothin’s wrong… I was just playin’ with ya.

34. How Many Chromosomes? You have a total of 23 pairs of chromosomes – Thus, you have 46 total chromosomes.

35. How Many Chromosomes Do Other Organisms Have? Penicillium (protist)= <4 Fruit Fly= 4 Mosquito= 6 Housefly= 12 Garden Pea= 14 Corn= 20 Frog= 26 Human= 46 Orangutan= 48 Horse= 48 Dog= 78 Fern= 1,262

36. Quiz ( Half Sheet of Paper ) 1.If there are 23 pairs of chromosomes in humans, how many chromosomes are there total? 2.What is the sex of this human karyotype? 3.Identify one problem with the genetics of this persons genome. 4.Which chromosome pairs below are homologous chromosomes? 5.What is different about these pairs of chromosomes? (be specific)

37. 1.Boy or Girl? 2.What’s wrong with this karyotype?

38. Edward’s Syndrome (Trisomy 18)

39. 1.Boy or Girl? 2.What’s wrong with this karyotype?

40. Patau Syndrome (Trisomy 13)

41. 1.Boy or Girl? 2.What’s wrong with this karyotype?

42. Angelman Syndrome (Maternal 15 deletion)

43. Objectives Distinguish between somatic cells and gametes. Distinguish between haploid and diploid cells.

44. Not all cells contain 46 chromosomes… Cell Types Somatic CellsGametes Body Cells – Contain 46 Chromosomes Sex Cells – Sperm & Egg Contain only 23 chromosomes (unpaired)

45. Gametes -Sperm/ Egg Gametes -Sperm/ Egg Somatic Cells -Body cells Somatic Cells -Body cells

46. Somatic Cells Normal Body Cells Contain 46 chromosomes (23 pairs) Diploid = 2 sets of chromosomes (mom & dad)

47. Gametes Sex Cells (sperm & egg) Contain no pairs, just 23 chromosomes Haploid = One set of chromosomes

48. HaploidDiploid Somatic Cells (Body Cells) Gametes (Sex Cells)

49. Gametes Combing During Fertilization Zygote =Diploid Gametes =Haploid

50. Haploid Diploid Haploid

51. Gametes