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.
Dinosaurs were the most awesome things to ever stomp the earth. I bet every one of us has wished at least once to have seen an Apatosaurus or T-Rex in the flesh, that’s why Jurassic Park is still constantly on TV 22 years after its release. Last year, scientists activated some ancient dinosaur genes lying dormant in their most disappointing descendent – the chicken – causing them to take on some dinosaur-like attributes. Humans are not descendants of dinosaurs, but we do share some common ancestors. How much DNA could the square and lowly Homo sapiens have in common with the rockstars of terrestrial life?
It’s rare that we stop and reflect on the sheer horror of life just 100 years ago before antibiotics, vaccines and sterile technique were commonplace. In those days, every meal was a game of Russian roulette with E.Coli and every sniffle from a child could spell their imminent demise. The 20th century has been a relatively safe haven from pathogens, but that might all come to an end soon, as drug-resistant diseases become more and more common, thanks to our misuse of medicine.
Over the years, multiple attempts have been made to eradicate Malaria, a disease responsible for millions of deaths. All attempts to date have failed, and malaria still affects an estimated 200 million people each year. This disease is becoming alarmingly adept at developing resistance to whatever drugs are thrown at it. Why is this, and why can all the drug resistant strains of malaria be traced back to the same point of origin – remote jungle regions of western Cambodia?
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.