There are many myths and misconceptions surrounding these little creatures. Some claim that the breeding of dwarf rats is unethical, while others argue that dwarf rats are just as healthy as their standard counterparts. There is far more proof pointing towards the latter - that breeding the dwarf gene, when done responsibly and properly, is perfectly okay.
The dwarf gene is very similar to the dumbo ear gene. It began as a spontaneous mutation in 1985. It is a recessive gene, meaning that 2 dwarf parents will produce a full dwarf litter, while 1 dwarf and 1 standard rat will produce a mixed litter. Dwarf rats lack the growth hormone, having approximately 6-10% that of normal rats. This keeps their size small while their proportions are completely normal. Dwarf rats are just as healthy as standards and due to the low concentrations of growth hormones, are actually much more resistant to tumors.
Dwarf rats remain tiny, ranging from 1/3 to 1/2 the size of their standard cousins.