The standard for Irish rats in some US clubs probably most closely resembles the UK Berkshire variety, though it is more accepting of rats with less white on their underside. The lesser marked versions are often given the affectionate but descriptive nickname “belly Irish” or “tummy Irish” in the UK – it is not a variety specifically bred for over here though, just something that occasionally turns up.
Genetics: Most likely as for Berkshire. Rats carrying one copy of the roan gene can also appear to be a type of American Irish , depending on other modifiers (Roro).
AFRMA standard: Irish rats may be shown in any recognized color. The top color is to be judged as to the respective color. Distinctive markings are the white underside, with four white feet and a white tail tip. The under marking should be a pure clean white, of moderate size and as even in shape as possible, not extending onto the legs, sides, or chest. The white feet should resemble the stops on a Dutch rabbit. The tail should be colored for most of its length, with a white tip of no more than one-fourth of its total length.