There are seven billion people alive today. The bible has been telling us for over a thousand years that every one of them is descended from just two humans, Adam and Eve. It’s interesting how often old stories we used to explain our world before science can strike a grain of truth! DNA that is passed from father to son on the Y chromosome, and mitochondrial DNA that is inherited from one’s mother, can both be traced back to single points of origin. As our understanding of population genetics in the world today grows, we get closer and closer to identifying our last common ancestors.
23andMe – the home genetic testing company backed by Google – have announced they want to use their data for drug development. I think this is a great idea, but a very important time for Google to remember their “Don’t be evil” policy.
What is 23andMe?
23andMe offer mail-order personal genome sequencing: you’re sent the kit, you take a swab of DNA from inside your cheek, send it back and wait for a copy of your own blueprints to appear online. What an age to live in! The data comes in the form of a ‘SNP panel’, meaning it tests for a long list of known single nucleotide changes that are common in the general population. The unique pattern of SNPs you have inherited can show you your ancestors paths across the world, as well as identify some nasty diseases you may carry or be predisposed to.
A South-African colleague of mine took one of the tests for fun. He was pleasantly surprised to find that the family rumour that his great-great-great grandmother was black were true, and that his whole family had inherited some of her black-african SNP pattern. He took great pleasure in announcing this at a family gathering, in front of some unpleasant racist relatives. Nothing annoys bigots like scientific proof that they’re ideas are bad and they should feel bad!
PRDM9 is my favourite gene. Why? Because it is the strongest driver of speciation identified to date. Thanks to the activity of PRDM9 (and probably some other similar genes we haven’t recognised yet), we live in a world full of awesome metazoans such as hedgehogs, dragonflies, narwhals and axylotils. The gene was tricky to find and it’s function is still not completely understood. Here, I will explain the story of it’s discovery, what we think it does, and why that’s awesome.
PRDM9 was only identified quite recently by scientists trying to understand the process of genetic recombination. [Recap paragraph!]: In my last post I spoke at length about how chromosomes can swap pieces of DNA with one another during cell division. I mostly talked about ‘non-homologous recombination’, where two chromosomes swap non-matching pieces of DNA with one another, one chromosome often completely losing vital genes and it’s counterpart gaining extras. Non-homologous recombination often causes disease, so why haven’t we evolved out of it? The reason is that homologous recombination – where two chromosomes swap like-for-like stretches of DNA – is an integral part of evolution, as it allows species to ‘shuffle’ different variations of genes and see which combinations work best together. The question is, what controls recombination? How does it happen?
Mutation is usually considered to be a random, uncontrolled process: Mistakes during replication cause random changes to the DNA sequence, which may have positive, negative or neutral effects on the organism’s survivability. Positive changes are sustained, negative mutations die off, neutral mutations just float about. Mounting evidence now suggests that mutation can also happen on a far grander scale than this, that the changes are not always randomly located, and that they may not be mistakes at all.
Evolution is not content with changing a species one base at a time: mutation can actually cause huge genetic changes over just a single generation. Whether these changes are adopted by the whole species (becoming ‘fixed’) is another matter, but it seems that rather than progressing via a gentle trickle of subtle changes, species try out all these small mutations in different combinations, shuffling their genomes about like a deck of cards.
This week’s blog post has been delayed while I participate in ‘I’m A Scientist – Get Me Out Of Here!’ a science communication competition in which schoolkids batter one with questions about science and life as a scientist. It’s been great fun but quite intense! Here are a couple of my favourite questions so far and my answers to them (pretty much all of which are about gene therapy):
Find me in the Bioinformatics zone! Blogging should resume next week!
Most genetic diseases are the result of a mutation that means a particular protein is made incorrectly, or not made at all. The idea of gene therapy is to infect cells – just how a virus would – with a small amount of DNA containing a replacement copy of the affected gene which slips into the cell’s genome and starts making the missing protein. The principle is elegant, but many challenges stand between the theory and successful use of gene therapy with real patients. In the last few years a number of advances have been made that have the potential to make gene therapy – something the medical community almost gave up on a decade ago – a powerful tool which could treat or even cure tons of diseases. What could be cooler than using the very tools viruses like HIV have painstakingly evolved to infect us with for our own benefit?
Your DNA says way more about you than a finger print, cigarette stub, boot print outside the window or any of the other evidence Sherlock Holmes always found so informative. DNA testing has been a great boon for criminal investigators, but is it always compelling evidence? Here are some notable occasions where the silver bullet that is DNA evidence has got jammed in the barrel of the gun of justice and messed everything up: