A Genetic Mutant?
Male cats can not carry the tortoiseshell markings—that is a genetic fact. This is based on very scientific principals, mainly that male cats only have one X chromosome. And, cats have this weird DNA twist: their sex chromosomes are directly linked to their fur color! (For more on this see this article)
It is important to recognize that multi-patterned calicos and tortoiseshell cats are already a result of a mutation process. This mutation occurs during the formation of the embryo. In order for this to transpire a female must start off with the Xb (black chromosome) and an Xo (orange chromosome) combination. While the embryo is developing a random switch between the Xb and Xo occurs resulting in a patchy coat pigmentation.
This means that a male tortoiseshell would actually be a double-mutant since he would need to inherit both the Xb and Xo chromosomes PLUS one Y (for him to be male). Quite a feat! Yet, mutations can occur but they are rare and the male is rendered sterile.
Now, imagine the excitement when a British veterinarian came across one of these wonders during a routine day in her practice. A client brought three tortoiseshell kittens to Dr. Karen Home’s clinic in Harpenden, Herfordshire for routine vaccinations. While examining the kittens, Dr. Home was happily surprised to discover that one of them was a male!
She immediately recognized that this kitten was indeed something special and adopted the little guy into her family of five cats, four dogs, and three children. They named him Eddie, after Eddie Izzard, the comedian because as Dr. Home said, “…. he is essentially a boy dressed as a girl.”