Features, characters, or developmental mechanisms/processes are epigenetic if they can only be understood in terms of interactions that arise above the level of the gene as a sequence of DNA. Since all phenotypic variation has a physical basis, we can define epigenetics at the molecular level as the set of modifications to our genetic material that change the ways of gene expression - switch on, switch off, or some intermediate stage - but which does not alter our genome which we can transmit in all its purity to our descendants. The sex of a crocodile or an alligator depends on the temperature during critical stages in the development of the egg - the same blueprint can be used to create either a male or a female croc.

McEachern and Lloyd [bh2]make the case that molecular epigenetic processes are amazingly conserved across metazoan phyla. The second (may be third)section presents several different levels at which epigenetic concepts are applied to development and evolution. There are even genuinely helpful diagrams, many with cute mice in them, to illuminate some of the more complex ideas.Nessa Carey has a PhD in virology from the University of Edinburgh and has had successful careers in both the university and commercial settings. Using the mammalian dentary as their example, they summarize what is known about the developmental basis for integration in that system. How is it that, despite each cell in your body carrying exactly the same DNA, you don’t have teeth growing out of your eyeballs or toenails on your liver?

But I had a tendency to wander off on routes that intrigued me - degree in Immunology, PhD in Virology, post-doc in Human Genetics, academic position in Molecular Biology. Nessa Carey, a molecular biologist, explains all clearly, while sucking in the uninitiated with intriguing tales of queen bees, tortoiseshell cats, un-identical identical twins and lots more.It is comprehensive in its coverage, generally well written and introduces basic information and concepts as they are required, rather than having a tedious ‘genetics 101’ chapter early on in the book, a feature of popular science books that often leads me to abandon them prematurely. However, they are functionally indeterminate in the sense that their complexity prevents us in most cases from creating frameworks that predict phenotypic outcomes directly from DNA sequences or sequence variation. This book provides an excellent introduction to a fascinating new field that may revolutionize our understanding of human health and disease. This was particularly fascinating as it shows how epigenetics, which seems like a very niche subject, is relevant to people in their day to day lives.

Here, the concept is used in the Waddingtonian sense and the emphasis is on the emergent consequences of interactions between developmental components. That said, there was much I did enjoy, especially her ability to switch between the nitty gritty account of lab work and a more abstract analysis of the scientific method. Just over a decade since Matt Ridley's seminal Genome, Nessa Carey presents a hugely compelling explanation of the very latest from the frontline of modern biology. This didn't last because I was allergic to fur, unable to think in 3D (not good for anatomy), quite bored and really rubbish at the course.This is a much more sensible metaphor, but then on the same page she refers to "the DNA blueprint" as if she hadn't read what she had just written. Chapter 6 by Gorelick, et al, presents what is, in some ways, a hybrid perspective between molecular biology and the older (classic? The epigenetic regulation of gene expression occurs through different cells having the same DNA blueprint but carrying molecular modifications which can be transmitted from mother cell to daughter cell during somatic cell division. And oddly enough I had always wanted to work at this end of crime - I must have been the only kid in the UK who had read a biography of Bernard Spilsbury by the age of 11.