Genetics In A Nutshell
Glossary
legal dispute (Jan 2003). Manipulating genes to produce children
Bases are the parts of DNA that carry the information to make
with specific traits such as eye colour, physical prowess or
and maintain a living thing. Most genes contain thousands of
musical ability is currently impossible.
bases. There are four different types of base, called A, G, T and
C (the initials of their chemical names). A group of three bases (a
DNA Deoxyribonucleic acid <pronounced 'dee-ox-ee-rye-bow
'codon') can carry the code for one building block of a protein.
new-clay-ick acid'> is the long chemical chain that genes are
made from. DNA contains two strands, twisted together into a
BRCA1 and 2 <pronounced 'bracca', short for 'Breast Cancer'>
double helix (a shape that looks rather like a spiral staircase).
are genes whose normal task is repairing DNA. When they go
Pairs of chemical units called bases stick these strands together
Genetics in a Nutshell
wrong, they are linked with some cases of breast cancer. Only 5
– their precise order, the DNA Sequence, determines which
to 10% of breast cancers are associated with these genes, but
proteins are made, and when. All the DNA in a living thing is
women with damaged versions of either of them have a 3 to 7
known collectively as its genome.
times greater risk of developing breast cancer.
This is the first instalment of the 'Science in a Nutshell'
Expression A gene is expressed when the information it stores
series, produced by the Science Media Centre. It is
Cell Every body is made of tril ions of tiny cells. There are
is used to make proteins, or to switch other genes on.
designed to be useful for busy news desks, especially
hundreds of types, each with a specialised job. Most cells have a
nucleus that contains a copy of the entire genome. Cells are
Functional genomics studies the relationship between proteins
those that lack ready access to a science
miniature chemical factories, built and regulated by genes.
and the genes that make them, in order to understand the role of
correspondent. 'Genetics in a Nutshell' provides you
every single gene (also see proteome).
with a clear explanation of some of the terms that are
Chromosome DNA is coiled into structures called
now used in stories about medical genetics.
chromosomes, found in the nucleus of each cell. Humans have
Genes carry the information to create everything from organs to
46 chromosomes - 44 are paired, and the other two are either XX
offspring. They determine your hair colour, your blood type,
It is intended as a handy guide, to be kept on your desk
(female) or XY (male) sex chromosomes. Each human
susceptibility to certain diseases and so on. Genes are made
chromosome can contain between 5 - 20 million bases.
from the chemical DNA. A gene can ultimately produce a
for use when genetics hits the headlines. It is not
particular protein, or act as the trigger to start other processes in
meant to teach you genetics from scratch.
Clone has several meanings: 1) An exact copy of a DNA
the body. Although we share many of our genes with other
molecule, as in 'to clone a gene' 2) More commonly, clone refers
animals, the actual DNA sequence of that same gene often
If you're stil not sure where to get the answers you're
to an entire living thing that is genetically identical to another.
varies between species - they are telling the same story with
looking for, or need to talk to a scientist about
Identical twins are natural clones, as are all the bananas in a
different words.
genetics, contact the Science Media Centre:
bunch. There are several different ways of cloning an animal.
Dolly the sheep was created by taking all the chromosomes from
Gene Therapy is a potential way of treating disease where
0207 670 2980 / smc@rigb.org
an adult sheep's cell, and putting them into an empty (sheep) egg
damaged or abnormal genes are replaced with normal ones.
cell. In the UK it is illegal to transfer cloned human embryos into
Although still quite experimental, there have been a few
www.ScienceMediaCentre.org
the womb to enable them to develop further. It is probably unsafe
successful cases. For example, Rhys Evans was born with a
to do so at the moment because these reproductive cloning
defective immune system, forcing him to live inside a sterile
"Imagine that the genome is a book.
experiments in animals produce many embryos that develop
'bubble'. Gene therapy on his blood cells repaired the fault in
abnormalities.
their DNA, allowing him to live a normal life. However, recent
There are 23 chapters, called chromosomes.
gene therapy trials in France seem to have caused leukaemia in
Each chapter contains several thousand stories, called
Therapeutic Cloning DNA is taken from a human patient to
two patients, casting some doubt on this technique. Germline
genes … Each paragraph is made up of words, called
make cloned embryonic stem cells, which many scientists
gene therapy applies the method to eggs or sperm, so that all
codons. Each word is written in letters, called bases."
believe could be useful for treating 'cell-loss' diseases like
the DNA in a resulting embryo is altered. This is not done in
Matt Ridley, from Genome: the autobiography of a
Parkinson's (this has, as yet, only been attempted in animals).
humans for ethical, practical and safety reasons.
species in 23 chapters.
The stem cells are turned into specialised cells for transplant,
which are unlikely to be rejected because they are an exact
Genetic Fingerprinting uses an individual's unique genetic code
genetic match with the patient. Therapeutic cloning is permitted
in criminal investigations or paternity cases. Most scientists
by UK legislation, but research is strictly regulated by the HFEA.
believe that it is very reliable - the odds of two people having the
same genetic fingerprint are about one in a billion.
Code The order of the bases in the working parts of DNA is a
code, which can be translated into instructions to make proteins.
Genetic Testing Kits can detect individual differences in DNA,
Hence we say that a gene 'codes for' a protein.
some of which may have medical importance. In the US, many
simple test kits are available from pharmacists, but their accuracy
Designer Babies A non-scientific term for children whose
is limited. Some claim that these tests may help people to tailor
genetic make-up has been altered or specially chosen e.g. by
their diet or medical treatment to their personal genetic profile.
selecting a particular embryo during IVF. This may help parents
The UK situation is under review by the Human Genetics
to avoid having a child with a genetic disease. If parents have a
Commission (Jan 2003).
sick child that could be cured by a special cell transplant, they
Thanks to: Prof Robin Lovell-Badge, Dr Matt Ridley, Prof Steve Jones, Roger
Genome The sum total of all your DNA. There are about 3
Watkins, Adrian van Klaveren, Tim Utton, Jacqui Thornton, David Shukman,
may choose to have another child with the correct genetic match
Keith Stafford, Ben Hirschler, Pat Reaney
by IVF (e.g. the Hashmi case), although this is still a matter of
billion base pairs in the human genome, which are organised into
30,000 to 40,000 genes. A map of the human genome allows
Sex Selection During IVF, it is possible to select only male (or
Gene Patenting A patent usually lasts for 20 years. If other
scientists to understand more about our body chemistry, and
only female) embryos for implantation into the womb. This is
people want to use the invention commercially, they need to
potentially helps them to tackle disease. The mouse genome has
currently illegal in the UK – however, sperm sorting is still
obtain permission from the inventor. A patent stakes a claim on
already helped scientists to improve their experiments on mice,
allowed, where sperm that will create a male child are separated
something useful, novel, and inventive. Human genes, as they
relating effects seen in this 'animal model' to human
from those that will give rise to a female. The HFEA are (Jan
exist in the cells of our bodies, cannot be patented because they
diseases.
2003) consulting the public about whether / how to regulate sex
are not inventions. However, copies of genes manipulated in the
selection.
lab can and do form parts of patents. In July 2002, the Nuffield
IVF or in vitro <"in glass"> fertilisation brings a sperm and an
Council on Bioethics concluded that genes have sometimes been
egg together outside the womb. Children conceived using this
Shotgun Sequencing is the method most often used to read a
patented too easily and that patents involving DNA sequences
technique are sometimes called ‘test tube babies’.
genome. It involves chopping the DNA into little pieces, working
should be the exception rather than the rule. Although patents
out what they all are and then getting a computer to fit all the
give companies an incentive to invest money in research, some
Junk DNA is that part of DNA that appears to serve no known
jigsaw pieces back together in the right order.
fear that non-commercial research may suffer as a result.
function. Although 97% of human DNA never actually makes a
protein, some of this can still be very important because it turns
Stem Cells have the potential to turn into many different types of
Genes For … We often hear about a 'gene for' something. But
nearby DNA on and off.
cell (described by scientists as ‘pluripotent’). Embryonic stem
if scientists discover a gene that is associated with a certain
cells can turn into any type of tissue – they are taken from very
condition, it doesn't necessarily follow that the gene is
Mutation Changes in a DNA sequence that may have a
early embryos that are about five days old, and comprise about
responsible for that condition. For example, most criminals are
profound effect e.g. mutations that cause cystic fibrosis.
100 cells. These embryos are not suitable to implant into a
male. They are male because of a small gene on their Y
However, many mutations will have no detectable effect.
womb. Adult stem cells, found principally in bone marrow,
chromosome. But that does NOT mean that this is the gene for
appear to be more limited in the range of cells they can turn into.
criminality, even though there is a high degree of association
Nucleus The information hub of a cell that contains the
However, there is still debate about whether embryonic or adult
between the two.
chromosomes.
stem cel s will ultimately be more useful. Stem cel s could be
collected to replace damaged tissue e.g. to treat Parkinson's
Contacts and Links
Phenotype Any physical effect (e.g. growing an arm, or
disease, in cancer patients, to treat blood disorders etc.
Science Media Centre 0207 670 2980
developing breast cancer) that is influenced by a gene.
www.ScienceMediaCentre.org
Transgenic Any living thing with artificially added or altered DNA
Human Genetics Commission www.hgc.gov.uk 0207 535 9930
Preimplantation Genetic Diagnosis/Screening When a
from another species is 'transgenic' e.g. the transgenic mouse
Human Fertilisation and Embryology Authority
couple plan to have children, they can take genetic tests for
with the cystic fibrosis gene. Such creatures may help scientists
www.hfea.gov.uk 0207 539 3330 / 14
inherited diseases. If they BOTH carry one copy of the gene for,
to understand, and perhaps treat, the disease. Other genes can
Biotechnology and Biological Sciences Research Council,
say, sickle cell anaemia, their child will have a 1 in 4 chance of
be changed so that an animal's organs are coated with human
www.bbsrc.ac.uk 01793 413 301
having the disease. If only one parent carries the offending gene,
antigens (chemical markers), allowing xenotransplantation
Medical Research Council www.mrc.ac.uk 0207 637 6011
their child is safe. This can help parents in planning a family. It
without rejection.
MRC Laboratory of Molecular Biology
may also prompt them to screen an embryo in the womb – if it
www2.mrc-lmb.cam.ac.uk
has a genetic disorder, parents may choose to abort the child.
Vector A virus used to carry a section of DNA into a cell e.g.
Wellcome Trust Sanger Institute 01223494956
Screening can present huge ethical dilemmas e.g. tests for
during gene therapy.
www.sanger.ac.uk
diseases with no cure; screening for disabilities.
Nuffield Council on Bioethics, 0207 681 6919 / 9627
Xenotransplantation Tissue transplant between two different
www.nuffieldbioethics.org
Proteins are chemicals that are essential for almost all life
species. Animal-to-human organ transplants have not yet been
Royal Society www.royalsoc.ac.uk/policy 0207 451 2516
processes. Genes carry the information needed to make
carried out.
Cancer Research UK www.cancerresearchuk.org 0207 061
proteins. Some proteins are enzymes that speed up chemical
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reactions in our bodies. Others can: carry messages between
Issues
Huntington's Disease Society of America www.hdsa.org
cells; control the activity of other genes or proteins; build
Cystic Fibrosis Trust www.cftrust.org.uk 020 8464 7211
muscle, hair etc.
Disease A few rare diseases are caused by a single mutation in
UK Patent Office www.patent.gov.uk 01633 814840 / 768 / 981 /
the DNA – just one faulty base out of about three billion e.g.
01372 363386
Proteome The sum total of all the proteins in your body.
cystic fibrosis or Huntingdon's disease. Others, such as
European Network of Patent Agencies gb.espacenet.com
Studies to explore what proteins do and how they are made,
breast cancer, are caused by a variety of factors including diet,
UK Forum for Genetics and Insurance www.ukfgi.org.uk
known as proteomics, will be the focus of much research for
exercise, age and genetic influence. Genetic tests might say if
020 7632 2177
decades to come and will help scientists to tackle disease.
someone is more likely to get a particular disease. In the future,
Genetic Interest Group www.gig.org.uk 0207 704 3141
this information might lead to better treatments for disease.
Progress Educational Trust www.progress.org.uk 0207 278
RNA (Ribonucleic acid) is a chemical cousin of DNA.
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Messenger RNA (mRNA) carries the genetic information stored in
Insurance In 2001, the government and the Association of British
National Centre for Biotechnology Information
DNA to the part of the cell that makes proteins.
Insurers established a five-year moratorium on the use of genetic
www.ncbi.nlm.nih.gov/genome/guide/human
test results in insurance. The Human Genetics Commission is
RNAi (RNA Interference) uses short sections of RNA to turn the
currently (Jan 2003) reviewing how insurers use 'family histories'.
www.yourgenome.org
effects of DNA on and off. This is a natural process in cells that
Insurance companies cannot ask individuals to take a genetic
www.ornl.gov/hgmis/project/info.html
scientists can use to understand how DNA works, and will
test. Insurance can only be affected by a genetic test is if you
www.ornl.gov/hgmis/publicat/primer2001/primer11.pdf
probably be the subject of many breakthroughs in the next few
have a family history of Huntington’s disease; a negative test
www.nih.gov/news/stemcell/primer.htm
years. Science chose RNAi as their 'Breakthrough of 2002'.
result counts in your favour.
Document Outline
