File talk:Knockout Mice5006-300.jpg

Not sure that the mouse in the picture is a good example of "A genetically modified mouse in which a gene affecting hair growth has been knocked out (left), shown next to a normal lab mouse". If so, please show the right reference for it.

It looks like they are showing a chimeric mouse (left) compared to a wild-type mouse (C57Bl6 strain). Chimeric animals are the offspring of the dams implanted with embryos with targeted stem cells (which are from a different strain -with different coat color- than the rest of the embryonary cells, hence the change in color).

Therefore, while it may very well be that the chimeric pattern is due to the mutation described, I believe it is not, even in that case, a very good representation of a genetically modified mouse.