Essentially however, the idea of a gene gym comes from the fact that the environment, and even the cells themselves, are all like gyms – they select the fit, from the unfit. Genes are the units of DNA that encode proteins, and it is proteins that are the building blocks of cells, and that conduct many of the operations needed to keep a cell alive.
I take bacteria that are absolutely identical, and then I change a single gene in one of them, just one gene from DNA that encodes thousands of genes. The particualr gene that I change, or actually add, to the DNA is a gene that makes the bacteria resistant to antibiotics – so it doesn’t die when given antibiotic medicine.
I then take the bacteria with an additional gene, and put it into a race with the original bacteria that doesn’t have the extra gene. The race is to see who grows best. As the only difference between the bacteria is a single gene, I’m really testing the fitness of the actual gene itself, and the ‘gym’ that I’m using is actually the cell that contains the cell, and the soupy broth that I grow the cells in.