Lecture 44 Prof Duncan Shaw

Recombinant DNA technology First technical breakthrough in medical genetics was chromosome analysis in 1950s Second is recombinant DNA, in the 1970s s This will culminate in the complete DNA sequence of humans (the Human Genome Project) There are now many methods available to analyse patients DNA in the lab, to identify mutations, to discover new genes, etc.

How to purify a gene First method is by cloning, i.e. introduce the gene into a bacterial cell then grow up large amounts and extract DNA (in vivo) Second method is by polymerase chain reaction (PCR) using DNA polymerase to amplify the gene in a test-tube (in vitro) Both methods have their uses but PCR is preferred in medical applications because it is quicker and cheaper

Bacteria provide the means Bacteria have been vital in developing DNA technology Thermus aquaticus (which lives in hot springs) provides DNA polymerase enzyme for PCR Escherichia coli (which lives in our guts) provides plasmids (mini-chromosomes) used in cloning 100s of bacterial species provide restriction enzymes that cut DNA at specific sequences of bases (4 - 8 bases long)

Applications In biomedical research - to identify the genes responsible for human characteristics (including disease) To analyse what goes wrong with these genes in disease (pathology) To provide prenatal and presymptomatic diagnosis, carrier detection, risk calculation New therapies (drugs, gene therapy)

95 o 50 o 72 o

Diagnosis by DNA of sickle-cell anaemia kb 1.1kb 1 = normal 2 = carrier (heterozygote) 3 = affected

DNA sequencing by the Dideoxy (Sanger) method