Explanatory primer for The Life Scientific with Prof Elizabeth Fisher
If you or someone you know is affected by a genetic disorder, you may be very interested in the episode of The Life Scientific with Prof Elizabeth Fisher on BBC Radio 4 on 12/11/19 (still available on BBC Sounds and The Life Scientific Podcast). She is a Professor of Neurogenetics at UCL who made the first ‘humanised’ mouse model of Down’s syndrome. It is a very interesting listen, however, the scientific terminology comes thick and fast and I thought it might be a bit easier to understand with a bit of a Genetics Made Simple style explanation!
Prof Fisher describes chromosomes as ‘these long, huge, enormous molecules that are found inside the cells of all of us’. Chromosomes are actually tiny! If you were to look at your skin though a microscope you would see hundreds of cells – that’s what we are made of. If you were to magnify that so that you could only see one cell, it would look a bit like a plum with a stone inside. Inside the ‘stone’ bit (called the nucleus) you have 23 pairs (46 in total) of chromosomes.
All your nucleuses have the same chromosomes in. The reason that to a molecular geneticist like Prof Fisher these are huge, is because within the context of the miniscule world of the cell, they are very big. The reason that they are big is because they contain a huge amount of information about how to make you and the things you need to function.
Chromosomes are made of DNA. DNA is a string-like substance (or molecule) that packages itself up tightly to form the chromosomes. If you unwind the string it can be read as a code containing all the information about making proteins. Proteins do all the work in the body, from making you digest to making you sleep. You make thousands of different proteins, and the DNA contains the information on how to make each one. Each instruction for a particular protein is called a gene. Imagine the chromosome is a recipe book, and the genes are the individual recipes.
X and Y
Prof Fisher is particularly interested in two chromosomes, the X chromosome and chromosome 21. We have 23 pairs of chromosomes and we get one of each pair from each of our parents.
Of the 23 pairs of chromosomes, 22 have nothing to do with whether you are a boy or a girl. These are the autosomal chromosomes. The remaining pair are called X and Y and determine if you are a boy or a girl. Boys are XY (they get an X from their mother and a Y from their father), and girls are XX (they get an X from their mother and a X from their father).
In the case of Turner Syndrome, the girl (it is only girls) only has an X chromosome, and therefore 45 chromosomes overall. So, they are missing a bit of genetic material.
In the case of Down’s syndrome, there is an extra chromosome 21, so they have 47 chromosomes, which is a bit too much genetic material. Part of the scientific interest in these two syndromes is therefore to do with research about ‘dosage’ of certain genes – ie making too much or too little of certain proteins because of the ratios of the genes compared to people with 46 chromosomes.
Prof Fisher talks a lot about mouse models. It can be understandably difficult to hear scientists discussing manipulating the genetic information of living animals in a dispassionate way, but these are an invaluable way of being able to work out what certain genes do in order to help humans with genetic disorders. There is a good explanation of why mice are used here: https://www.yourgenome.org/facts/why-use-the-mouse-in-research. Also, it is important to know that a lot of thought, reasoning and ethical planning go into the decision to use mice in any experiments.
I hope this bit of information lays the foundations to understand more about Prof Fishers work. If there are any of the more complicated concepts that you would like to understand more about, please do contact me at firstname.lastname@example.org
Other useful links
Turner Syndrome Society: https://tss.org.uk
Down’s Syndrome Association: https://www.downs-syndrome.org.uk