The genome is the term that describes the total
genetic material of an organism - all the DNA.
The human genome projects has mapped and
identified all the genes found in human DNA.
Every organism has its own unique genome
and scientists can now completely work it out - clever stuff!
Genome data is used to characterise species and
help research plant and animal evolution patterns.
See note 3. below on the human genome.
The human genome has around 3 billion base
pairs in the DNA sequences of the genes-chromosomes!
Apparently quite a lot of your DNA is 'junk',
but don't worry, and we won't go into that, just study hard, play
hard and enjoy life!
Thousands of scientists around the world have
collaborated on the human genome project.
We now know the complete human genome and over
20,000 to 25,000 genes have been located on it, but although
we know what many do (code for), there is much more to find out.
Around 1800 genes have been identified that
relate to human diseases - and this data is the target of medical
research to benefit medicine.
PLEASE NOTE that all humans share 99.9% of
their genomes, which makes you think!
How is our understanding of the human genome
helping science
e.g. evolution theory or medicine?
Any new drug must be targeted
at some specific medical condition where there is a need.
The target might be blocking the
action of an enzyme or a gene with a chemical agent (drug) you can
interfere with the development of a disease e.g. the anti-cancer
drugs used in chemotherapy treatments to reduce the growth of tumour
cells or kill them.
Studies of the genomes and
resulting proteins in both plants and animals are proving useful to
identify 'targets'.
You then have to find a chemical
that will have an effect on the target, fortunately there are
databases of chemicals that have been previously screened for likely
effectiveness.
The screening might not initially
indicate the best molecule to 'hit the target' in a biochemical
sense, but, it may provide a starter molecule - which you can then
modify to make different derivative molecules, one of which might
provide a more effective treatment.
Medical applications
e.g. prediction and prevention of
disease, testing for and treating inherited diseases, more effective
medicines, BUT, there are ethical issues to deal with too.
1. It has been possible for genetic
scientists to identify particular genes (genetic variants) in the genome that are linked
to certain types of non-inherited diseases.
Hopefully it will lead to predicting
predisposition to certain diseases, leading to early
intervention with medical treatment and perhaps a preventing
disease actually developing.
If you know what genes predispose people
to certain diseases, medical advice can be more accurately given
e.g. choice of diet and other lifestyle factors based on the
results of genetic screening tests.
Many common diseases like cancer and heart
conditions are caused by the interaction of different genes, as
well as lifestyle factors.
See also
Introduction to genetic
variation - formation and consequence of mutations
and
Stem cells and uses
- leukaemia treatment
2. From the human genome project, by knowing the
genes associated with
an inherited disease
(genetic disorder), we can understand it more clearly and
then develop more effective treatments - which may involve
genetic engineering itself.
We know inheriting certain genes greatly
increase your risk of developing certain cancers, this can help
with making lifestyle choices to minimise the risk of suffering
from the disease - as with 1. above, its a sort of risk
management situation.
In the UK newborn babies are routinely
tested for particular genetic variants known to cause genetic
disorders e.g. the double recessive allele that causes cystic
fibrosis.
The results from genetic screening
enables the medical treatment-management to begin promptly
while the baby is still very young.
Children with leukaemia can have a genetic
test to help decide which is the most effective treatment in
terms of medication and its dose.
See further notes on
genetic screening of an
embryos or fetus
and
Introduction to the inheritance of
characteristics and inherited disorders
It is hoped that all this new genetic
science will lead to the development of better, and more
personal, treatments for a wide range of medical conditions.
We are now developing drugs and other
techniques that work at the molecular level in combating
disease and tailored to suit the individual's body
chemistry.
The variations in patients genetic
variants (alleles) mean that one drug isn't necessarily as
effective with all patients suffering from the same
condition - so new drugs can be designed to suit these
'varying' patient situations.
3. We know certain alleles affect how
our body responds to certain diseases and their treatment.
Scientists hope to use this knowledge to
develop more effective drugs that can be specifically suited to
patients with certain alleles in their genome.
Different drugs can be tested, and their
effectiveness compared with the patient's alleles, and you can
compare existing drugs with new ones.
It has been found that some breast cancer
drugs are only effective in women if they have certain alleles
in their genome.
4. To help in these medical quests,
scientists are analysing the genomes of human pathogens to help us
understand and control certain infectious diseases.
The complete genome of bacteria such as
the deadly MRSA, which is resistant to antibiotics.
It is hoped that pathogen genome knowledge
will allow swifter decisions as to the best treatment
administered to patients i.e. determined by the genomics of the
specific bacterial strain.
The science of human evolution
and migration
The human genome project can be tackled by
various genetic strategies.
(i) Analysis of data from people's Y
chromosome inherited down the male line.
(ii) Analysing mitochondrial DNA inherited
through mothers.
Our knowledge of the human genome is
being used to trace the migration of certain populations
across the continents of the world.
The latest research suggests that all
modern humans have descended from a common ancestor who lived in
Africa, and their descendents have spread over all over the
Earth - moving by both land and sea.
This is known as the 'Out of Africa'
theory and seems to have begun around 60 000 years ago.
Why did this happen?
Maybe change in climate, so
seeking more food for hunter-gathering tribes?
It is known the climate in Africa
at this time became much dryer - less rain, less plant
life, less food for animals, less plants and animals for
humans to eat.
All humans have a very similar genome.
In terms of ancestors - genetically, who you were and
where you have been is 'hidden' in your genome! until, that is,
modern DNA analysis reveals all !!!
However, as different populations of
people migrated to different areas of the planet, small
differences in DNA 'evolved' (incorporated) into their
genome e.g. producing different skin or hair colour or
facial features.
The genetic variation is as little as
0.001%, but even so, genetic scientists can work out when
these new populations split off in a different 'genetic' and
geographical direction.
People who are related will have an
even more similar genome.
The human genome is being compared to some
of closest relative in the world e.g. primates.
Ever since researchers sequenced the chimp
genome in 2005, they have known that humans share about 99% of
our DNA with chimpanzees, making them our closest living
relatives - that should make you think!
