Genome mapping and DNA technologyIB MYP Biology: Revision notes

A genome is the complete set of genetic material (DNA) in an organism. The Human Genome Project (1990-2003) was an international project that worked out the order of all the bases in human DNA. This is called genome sequencing.

The project found that humans have about 20 000 genes. Sequences of other organisms, such as mice, bacteria and crop plants, have also been found.

Uses:

• Finding genes and alleles linked to inherited disorders
• Developing genetic tests and new medicines
• Matching treatments to a person's genes (personalised medicine)
• Tracing human migration and evolution

A DNA profile (genetic fingerprint) is a pattern of bands that is unique to a person, except identical twins. It is made like this:

1. Take a sample (blood, hair root, saliva) and extract the DNA.
2. Cut the DNA into fragments with enzymes.
3. Separate the fragments by size using gel electrophoresis, which gives a pattern of bands.
4. Compare the pattern with other profiles.

Because half of a child's DNA comes from each parent, each band in a child's profile must match one of the parents.

• Forensics: match blood, hair or saliva from a crime scene to a suspect, or rule a suspect out.
• Paternity testing: find which man is the father of a child, because the child's bands that do not match the mother must match the father.
• Identifying remains of disaster victims, and tracing relatives.
• Conservation: checking how closely related animals are.

A match shows that the DNA came from that person. It does not show when it was left or that the person committed a crime.

Genetic testing looks for faulty alleles in a person's DNA. Genetic screening is testing groups of people, such as all newborn babies.

• Newborn screening finds disorders early so that treatment can begin.
• Carrier testing shows if someone carries an allele for a disorder, such as cystic fibrosis, that they could pass on.
• Embryo screening checks embryos made by IVF before one is placed in the uterus.

Benefits: early treatment, informed choices. Issues: anxiety, false results, privacy of data, discrimination by insurers or employers, and decisions about ending a pregnancy.

Gene therapy is an experimental treatment for inherited disorders. A working copy of a gene is put into a patient's cells (often using a harmless virus) to make up for a faulty allele.

• It treats the cause of the disorder, not just the symptoms.
• Only the treated cells are changed, so the effect can wear off and the treatment may have to be repeated.
• Risks include the gene going into the wrong place and an immune reaction.
• It is still mostly in trials and is expensive.