This is a story about a gene which makes nursing mice produce more nutritious milk while also making their offspring less demanding. The gene serves to balance nutrient supply and demand between the mother and pup. If the gene is knocked out, the mother’s milk is less rich, but the pups are more demanding, evening out the impact. Things only go wrong when there’s a mismatch. If pups with a defective copy of the gene feed from a normal mother, their increased demand makes them grow larger than normal. Conversely, pups with a good copy end up smaller if they feed from a mother lacking a working copy, since her milk is less nutritious. Continue reading →