The introduction of a 'dilute' gene at some unknown point in history has resulted in silver-toned chocolate Labs and dilute-colored black and yellow Labs. These colors are not officially recognized by the AKC, and controversy surrounds these unique colorings. Some believe Weimaraner genetics may exist in the bloodlines of a silver, grey, or otherwise dilute Lab, though this idea has not been substantiated.
It has been shown that out of all dog breeds, it is the Labrador Retriever that is most likely to be obese. In a 2016 published study it was shown that out of 310 Labradors, most were missing all or parts of the POMC gene. This gene plays a part in appetite regulation as well as indication of the amount of one's stored fat. The study concluded that the absence of that gene had a significant impact on Labrador weight and appetite. The POMC gene mutation is present in only one other breed – the Flat-Coated Retriever.