-An undergraduate from Utah
April 7, 2011
Yes fat, yellow mice can have thin brown pups. Even if their genes make it look impossible.
How can the pups be brown when their genes tell them to be yellow? By the environment marking the genes involved and changing how they work.
Before getting into this, let's first talk about the genes involved in how pups end up yellow or brown. Then we can delve deeper into how the environment can change how a gene works.
Yellow is Dominant
Agouti is one of the key genes involved in making a mouse brown or yellow. Small differences in the versions of the agouti gene cause differences in colors or hair patterns. So one version, the dominant agouti gene (A), directs cells to make the yellow pigment and the recessive version (a), tells them to make a brown pigment instead.
For example, scientists have found that changing the diet and toxins that pregnant mice are exposed to can change the expression of the agouti gene in their pups. So in addition to the genes the moms hand down to their offspring, they also pass an 'epigenome' along. And the epigenome depends on what the moms are exposed to in their environment.
When scientists fed pregnant yellow mice diets rich in nutrients containing methyl-groups, like folic acid and vitamin B12, the agouti gene in pups got switched off. And the pups from such mice were brown and thin, not fat and yellow.