Dwarf

Science has described three different dwarfing genes in rats, all of which have their associated health problems and fertility problems. At several points the fancy has had reports of dwarfed rats who are completely fertile and with no associated health problems. The dwarfism in all the reports I have founds seems to be caused by a simple recessive gene, with both sexes reaching half size (160-170g for does and 200-270g for bucks). Adult size seems dependant on modifiers, with dwarfs from dwarf parents being smaller than dwarfs from carrier parents.

I am not aware of anyone currently breeding dwarf rats.