1. 3.2 Chromosomes

2. 3.2 Objectives
Prokaryotes have one chromosome consisting of a circular DNA molecule.
Some prokaryotes also have plasmids but eukaryotes do not.
Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
In a eukaryote species there are different chromosomes that carry different genes.

3. Prokaryotes V Eukaryotes chromosomes
Circular Naked DNA (no proteins)
Linear DNA
Plasmids
DNA associated with Proteins (histones)
Nucleoid region
Nucleus

4. Plasmids Plasmids are small extra circular DNA molecules
Found in some Prokaryotes but not in eukaryotes
Can contain genes but not for functions of life.
Eg: Genes for Antibiotic resistance
Useful for gene transfer/cloning
Insulin production (Biotechnology)

5. Prokaryotes 1 circular chromosome
Only 1 copy of each gene
Replication is the same as but only for 1 gene

7. Eukaryotes Linear chromosomes DNA and histones (8+1)
Genes found on different chromosomes
Visible during mitosis but not during interphase
23 different types of chromosomes (in pairs, mum and dad)
Specific chromosome and loci for each gene

8. Eukaryotic chromosome structure

9. Homologous Chromosomes
Are types of chromosomes that carry the same sequence of genes
However they are not usually identical as the alleles can be different.
A species have the same number of chromosomes with the genes are the same loci, this is what makes them able to breed and produce viable offspring.

10. Karyogram

11. Creating a Karyogram Amniocentesis CVS Slight risk involved in both
Amniotic fluid
CVS
Placenta
Slight risk involved in both

12. Meiosis I Animation
Meiosis II Animation

14. Link to Youtube scan.

17. 1.

18. 2.

20. Cairns’s technique
So how do we know how big chromosomes are?

21. Cairns’s technique
Cells were grown in a medium of tritiated thymidine (radioactive isotope of hydrogen)
Cells placed onto dialysis membrane and the cells walls digested, their DNA was released onto the dialysis membrane
A thin photographic film was applied to the dialysis membrane and placed in darkness for 2 months

22. After 2 months, the film was examined and the places where the tritium decayed their was a dark mark indicating the position of the DNA.

24. Activity
G/Drive: Karyotyping online task

25. HW: Notes, Quiz next lesson 3.1 and 3.2