1. 3.2 Chromosomes

2. 3.2 Chromosomes Understandings:
Prokaryotes have 1 chromo consisting of circular DNA
Some prokaryotes also have plasmids but eukaryotes do not
Eukaryote chromo’s are linear DNA molecules associated with histone proteins
In a euk species there are diff chromo’s that carry diff genes
Homo chromo’s carry the same sequence of genes but not necessarily the same alleles
Diploid nuclei have pairs of homo chromo’s
Haploid nuclei have 1 chromo of each pair
The # of chromos is a characteristic feature of members of a species
A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
Sex is determined by sex chromos and autosomes are chromos that do not determine sex

3. Understanding: Prokaryotes have ONE chromosome consisting of a circular DNA molecule

4. Understanding: Some prokaryotes also have plasmids but eukaryotes do not

5. Bacterial Plasmid

6. Multiple Resistance Plasmid

7. MRSA = multiple resistance Staphylococcus aureus

8. Understanding: Eukaryote chromosomes are linear DNA molecules associated with histone proteins

9. Nucleosome Subunit of eukaryotic chromosome
Consists of 8 histone proteins
DNA wraps around histones twice
Function: Supercoils DNA around histones to pack it into a small nucleus

10. Understanding: In a eukaryote species there are different chromosomes that carry different genes

13. Understanding: Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes

15. Understanding: Haploid nuclei have one chromosome of each pair

16. Understanding: Diploid nuclei have pairs of homologous chromosomes

17. Understanding: The number of chromosomes is a characteristic feature of members of a species

18. Sex is determined by sex chromosomes & autosomes are chromosomes that do not determine sex

19. A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
Karyotype
Karyogram

21. Karyogram of egg vs sperm: Sperm have 2 possible karyograms

22. Male or female? Normal or disorder?

23. Male or female? Normal or disorder?

24. Turner Syndrome

25. Klinefelter Syndrome

26. Superfemale!

27. Down’s Syndrome

28. Down’s Syndrome characteristics

30. Nature of Science: Developments in scientific research follow improvements in techniques: Autoradiography was used to establish the length of DNA molecules in chromosomes.
Images, rather than quantitative data, provide evidence
Autoradiography used since 1940s to discover where substances were located in cells or tissues
John Cairns used autoradiography differently in 1960s – got images of whole DNA molecules from E. coli and discovered that bacteria have a SINGLE CHROMOSOME and showed replication forks
Cairn’s technique was used by other scientists to discover structures in eukaryotes

31. Application: Cairns technique for measuring DNA length using autoradiography

32. John Cairns

33. Cairn’s autoradiography technique
Radioactively labelled DNA (tritium – radioactive isotope of H) produced by E. coli
DNA released onto surface of dialysis membrane
Thin photographic film applied to membrane and left in darkness for 2 months, which some DNA decays and emits high energy electrons that react with film
Film developed and examined with microscope. Where each tritium atom decayed there is a dark grain, showing DNA