BioMed
UK scientist Nessa Carey explains how cells with the same DNA become retina or bladder cells, and why gene regulation matters for inheritance.
Nearly every cell in the body carries the same DNA, yet the body is built from tens of trillions of cells forming tissues that are completely different from one another. The difference lies in which genes each cell switches on: a retina cell uses a different set of genes from a bladder cell. This explains why a cell holding the full instructions for a whole body does not build one.
The best science often starts with a question so obvious that almost nobody thinks to ask it. One example is why mammals need both a male and a female parent to reproduce. Questioning what everyone takes for granted can open up a whole field.
Nutrition has dramatic effects on how healthy mammals are and how long they live. Cutting calories over a long period can extend a mouse's lifespan by as much as a third. Mouse results do not automatically carry over to humans.
The systems that switch genes on and off are not neatly designed. They are layered networks built from reused, multi-purpose parts, and they are absurdly complex, like a contraption assembled from whatever was lying around.
Cells read their genetic code more like a script to be interpreted than a mould that gives the same result every time. So mapping an organism's full genetic code is not enough to predict how it will develop or behave, despite talk that the code explains everything.
Upbringing and surroundings combine with inherited genes to produce what an organism becomes. The book uses this to help explain why hardship and trauma can leave lasting effects on a person's body and life. It also warns that most of this field is still young, and many popular claims run ahead of the evidence.
Organisms with exactly the same DNA can still differ in what they look like, how they work and which diseases they get. Identical twins are the clearest natural test. Whatever separates them cannot be written in the gene sequence, so it must come from how those genes are used.
Scientists can, and often do, keep believing a theory long after there is enough evidence to discard it. Old explanations hold on until the weight of contrary findings forces a shift.
Many major scientific advances began with a fairly chance event rather than a planned search. An unexpected result, noticed by the right person, can redirect a whole field.
Press coverage makes cloning mammals sound routine and easy. In reality, making a clone by moving the core of an adult cell into an egg is still slow, laborious and expensive. Turning a specialised adult cell back into one that can build a whole animal remains difficult.