3.2 Chromosomes

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.

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

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)

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

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

Eukaryotic chromosome structure

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.

Karyogram

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

Meiosis I Animation Meiosis II Animation

Link to Youtube scan.

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

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

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.

Activity G/Drive: Karyotyping online task

HW: Notes, Quiz next lesson 3.1 and 3.2