Advances since Watson & Crick

Applications of DNA Technology DNA fingerprinting in forensics Human Genome Project

DNA Fingerprinting Every individual (except identical twins) has a unique DNA fingerprint These “fingerprints” can be used in forensics to help determine possible suspects in a crime What kinds of cells are used for the collection of DNA evidence?

Kinds of Samples They can use: –Hair –Skin –Saliva –Blood (Why can’t red blood cells be used?) –Semen –Vaginal Secretions What are the steps a forensic scientist would use if he/she found a hair at a crime scene?

Step 1: Amplify the DNA There is not enough DNA in one hair to identify the “fingerprint,” so many copies of the DNA need to be made PCR (polymerase chain reaction) is the process used to make billions of copies of the DNA This process can be used on impure, non- living samples and only takes hours

Step 2: Cut the DNA Restriction enzymes cut DNA at specific locations For example: The restriction enzyme EcoR1 cuts the DNA at the sequence GAATTC, between the G and the A

Step 2, cont’d. The two samples in the example are from different sources, so the cuts happen in different places. The result is that the DNA is cut into fragments and the lengths will vary with individuals.

Step 3: Gel Electrophoresis Once the DNA has been cut, it can be separated into bands (based on their size) by using gel electrophoresis. This technique involves loading the DNA sample (which is made up of lots of fragments) into the negative end of a gel. The DNA fragments move towards the positive end as a current runs through the gel (remember, opposites attract!).

Step 3: cont’d. Fragments of DNA settle out in the gel and form bands. Large fragments don’t travel as far as short fragments. These bands can be seen after staining and destaining the gel.

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Step 4: Genetic Markers Cutting an entire genome will produce thousands of bands to study– a way to reduce the amount of work forensic scientists is to use genetic markers. Genetic markers occur on particular stretches of non-coding DNA that are unique to each person. These are the areas that are analyzed for court evidence.

Human Genome Project In 1990, The Department of Energy, The National Institutes of Health, and the private sector began work on mapping the entire human genome. The organizations planned for this project to take 15 years, but it was completed in 2003.

Human Genome Project, contd. Project goals: –identify all the approximately 20,000-25,000 genes in human DNA, –determine the sequences of the 3 billion chemical base pairs that make up human DNA, –store this information in databases, –improve tools for data analysis, –transfer related technologies to the private sector, and –address the ethical, legal, and social issues (ELSI) that may arise from the project. –

DISCUSSION TIME! What do you think the implications of the Human Genome Project are? What advances in science can now be made because the genome has been mapped? What are the pros and cons of this knowledge?