|Two variants of the agouti gene: yellow on the left and a wild type on the right|
|My three mice: Pepper (black piebald longhair), Poppy (black piebald, wild coat), and Ginger (lethal yellow satin)|
|Ginger before her weight gain|
Lethal yellow is a gene that has been used rather heavily in scientific research. Why? Along with the golden coat, this form of yellow causes obesity, insulin-resistant diabetes-like traits, and an increased likelihood of developing tumors, among other things. Understandably, this has lead to lethal yellow lab mice being used in the research of diabetes. Interestingly enough, unlike some other mouse colors, dominant yellow had existed among fancy mice for a very long time, their usefulness for research only discovered some time later.
At first glance, most people would look at a dominant yellow mouse and say, "Isn't that pretty!" without having any idea of what else that color means. If I had previously known what this color meant, I might have decided against bringing my lethal yellow home. In all likelihood, she will live a shorter life than her sisters due to the pure chance of her being born a dominant yellow.
|Thanks to its blue eye, this cat is probably deaf in one ear.|
The white spotting genes (causing tuxedo, etc.) also can lead to deafness, but this is not seen as frequently as deafness in dominant white cats.
There are countless other instances of pleiotropy out there, some of which have not been confirmed through research. Correlation implies pleiotropy, and many genes correlate with secondary traits.
Sources are Genetics, North Dakota State University, PubMed, University of Tennessee at Knoxville, Genetics (second article), Berkeley, Louisiana State University, and MessyBeast. Images are from Wikimedia Commons with the exception of the photographs of my own mice and are under Creative Commons licenses: 1, 2.