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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 - 1990s
• 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)
95o
50o
72o
1
2
3
1.3kb
1.1kb
Diagnosis by DNA of sickle-cell anaemia
1 = normal
2 = carrier (heterozygote)
3 = affected
DNA sequencing by the
Dideoxy (Sanger) method