What is your Genome?
Your body is made up of millions and millions of cells.
Inside a cell is one Cell Nucleus and thousands of Mitochondria.
Inside the Cell Nucleus there are 46 Chromosomes, which can be grouped together into 23 pairs.
Inside every Mitochondrion there is one Chromosome, although there may be several copies of it.
A Chromosome is a structure holding information passed on from parents to their children.
This information defines what the human body looks like and how it works. It is what differentiates a human from a chicken or an oak tree.
A lot of the information is called Genes. A Gene might determine your blood group, skin color, eye color, hair color and so on.
Many things about you are more complex. They are not decided by just one gene. They might be controlled by a large number of genes working together.
Plus, of course, your environment has a huge impact on how your body develops and works, for your whole life from before birth onwards.
Chromosomes in the Nucleus
These chromosomes are often called Nuclear chromosomes to differentiate them from the chromosome in the Mitochondria.
Doctors can see Chromosmes under a microscope, and they can use chemical stains (or dyes) to highlight light and dark bands on the chromosomes. The size, shape and banding patttern is what lets scientists match the chromosomes into pairs. The picture below is a photograph of a man’s 23 pairs of chromosomees.
You can tell it is a man’s chromosomes because pair 23 does not match exactly. It has one X Chromosome and one Y (smaller) chromosome. If pair 23 had two X Chromosomes instead, this would be from a woman.
Why do we mattch these chromosomes into pairs?
For each pair of chromosomes, one has come from your Mother and one has come from your Father.
In the case of pair 23, a man’s Y chromosome must have come from his Father, since his Mother must have had two X Chromosomes.
Putting the Y chromsome aside for a moment, each pair of chromosomes carries the same set of genes.
For example, Chromosome 9 carries the ABO Blood Group Gene.
This means that you carry two copies of this gene, one on each chromosome of the pair.
Each of these copies can have one of three values called A, B or O.
Your blood group is determined by combining the two values. If you had version A on one chromosome and version B on the other, your combined value is AB.
If your combined ABO gene is AA, AO or OA, you will be blood group A.
If your combined ABO gene is BB, BO or OB, you will be blood group B.
If you combined ABO gene value is AB or BA, you will be blood group AB.
If you combined ABO gene value is BB, you will be blood group B.
if you combined ABO gene value is OO you will be blood group O.
DNA is the very special chemical inside every chromosome which actually holds the genetic information.
It is a special chemical because it can hold a vast amount of information in a compact form, is very stable and can be copied reliably.
The exact structure of DNA is complicated, but we can think of it as a hige chain. Each link in the chain is made up of one of four chemicals called Bases. Doctors represent the four bases with a letter, A, C, G and T.
The information is held in the order and position of these bases.
Doctors can represent DNA as a long list of these letters.
Because analyising some DNA means finding out its chemical make up and writing it out as a sequence, doctors and scientists call this process Sequencing the DNA.
Your genome is all of the DNA in the 46 Nuclear chromosomes and the Mitochondrial chromosome.
There are about 23,000 Genes in your Genome.
These are almost all in the Nuclear DNA – the Mitochondrial Chromosome only holds 37 genes, all to do with chemical processes to release energy from food inside the Mitochondria.
Until very recently, analysing DNA accurately was a long, cumbersome and very expenjsive process.
At one time doctors thought that the only important DNA was the part representing these 23,000 genes, and the rest of the chromosome was “junk”.
They have now found that the other DNA, not directly holding genes, is actually very important. For example some of it holds control information that can “switch on” or “Switch off” genes.
The study of this additional DNA and how it works is called EPIGENETICS.
That is why they use the term “Genome” and not just “Genetic” – it is not just about the genes, it is about all of the DNA. All 3,000,000,000 letters of it!
Because of better knowledge, better techniques, computers and automation the cost and time to analyze DNA is reducing all the time.
In the 20th century, doctors made huge advances in some diseases because of their research into Genetics.
Doctors worked out the rules of Inheritance for some genes in the Nuclear DNA , studied famililes with genetic disorders and began to analyze the risk of children inheriting diseases.
Understanding chromosomes led to pre-natal testing for some disorders, and near-natal testing for others.
Some people could be given treatments before their disorders developed.
Genome Research aims to develop the same kind of understanding for the entire human genome. That means all the control information as well as the genes themselves. It also means looking at disorders associated with multiple genes, which are difficult to understand by looking at a small number of genes one at a time.
Genetic Medicine or Genetic Coulseling takes our understanding of Genes and applies it to people.
Genomic Medicine will take our understanding of the whole DNA Genome and apply that to people.
Genomic Testing looks at all of the DNA of a group of people , some with a disorder and some not, and look for all of the patterns, not just one or two genes.
Genomic Medicine will try to look at all of a patient’s DNA and predict:
- Possible new therapies for their disorder
- Possible adverse side-effects for treatments
- the best dosage for a drug to balance positive effect and negative side-effects
The UK 100,000 Genome Project
The UK Government has set up a massive medical research program to develop genomic medicine in the UK. It will be delivered by a government-owned company called Genomics England.
This program will recruit around 70,000 people willing to provide Blood samples for DNA analysis plus full medical records.
All of this information will be turned into data so it can be analyzed by sophisticated computer programs.
Many of the recruits will have cancers or rare diseases.
The computer analysis will try to find DNA patterns associated with a cancer or a rare disease, but not found in the genral population.
The DNA might be in one or more genes, it might be in control information, or both.
Doctors will look for DNA patterns which can:
- the underlying source of a disorder.
- make a person more likely to develop a disorder
- make a person less likely to develop a disorder
- indicate a possible treatment
- indicate reasones for drug reactions or adverse side-effects
All mitochondrial disorders are in scope and will be studied by the 100,000 Genome Project.
This includes LHON.
Genomics England has been running various education and pilot projects already.
The main recruitment and delivery of the Project will run from 2015 to the end of 2017.
This page was last updated September 9 2015