Sequencing genomes
A genome is the complete set of genes in a cell. Improvements in sequencing technology allow genetic material from a wide range of organisms, including humans, to be analysed.
Once a genome has been sequenced, researchers can investigate the roles of genes and how different genes interact. The sequence data can also be compared between organisms and between individuals.
Producing a reference genome
A reference genome is produced by sequencing DNA from several members of the same species and comparing their base sequences.
Combining information from several individuals reduces the effect of an unusual mutation or sequence variant found in only one organism, making the reference more representative of the species.
Exam Tip: If asked why several individuals are used to produce a reference genome, explain that a sequence variant present in one individual may not be typical of the species as a whole.
The Human Genome Project
Work on the Human Genome Project (HGP) started in 1990, with research groups in several countries contributing human DNA sequence information to a shared reference genome.
| Feature | Key point |
|---|---|
| Funding and access | Public funding was intended to avoid commercial control of the project, and the resulting sequence information was made available for researchers to use and share. |
| DNA samples | The reference incorporated sequence information obtained from more than one person. |
| Progress by 2003 | By this point, the human sequence had reached about 99.9% accuracy. |
| Genome size | More than 3 billion base pairs were present in the assembled human sequence. |
| Gene number | The initial estimate was about 25,000 genes, considerably fewer than researchers had anticipated. |
Genome-wide comparisons
Complete genome sequences can be compared at two important levels.
Between species
Patterns of similarity and difference in DNA provide evidence about evolutionary relationships. Genome comparisons can also contribute to medical research.
Between individuals
Sequence variation between people can be investigated in studies of human disease and can contribute to personalised medicine based on an individual's genome.
Medical uses and ethical issues
Access to human genome information creates potential medical benefits, but the same genetic information also raises ethical questions about how it should be used.
Potential benefits
- Screening for DNA variants associated with inherited disorders.
- Identifying people who are carriers of particular genetic conditions.
- Using pre-implantation screening before an embryo is implanted.
- Testing for some inherited disorders before clinical symptoms appear.
Ethical concerns
- Genetic results could be used to discriminate against individuals.
- Personal genetic information could be used inappropriately.
- There are questions about who should own or control a person's genetic information.