American Fancy Rat & Mouse Association

This article is from the Fall 1997 AFRMA Rat & Mouse Tales news-magazine.

Colors & Coats

Cap-Stripe Lethal?

Q About a year and a half ago I purchased a Cap-Striped male rat. He was white with a patch of color on either side of his head which covered the ear, the eye, and the cheek with a wide band of color from the base of his neck to his tail. The color was divided by a white collar around his neck. Because I liked this particular patterning, I decided to try to reproduce it.

“Marbles Image,” daughter of “Marbles”

The first breeding was to a self colored female because I did not have access to a Cap-Striped female. She produced a litter of 18, with a variety of coat patterns, including several Cap-Stripes. I kept one of the females for breeding.

When bred back to the original male, she produced a litter of only 6, of which 2 were stillborn and none were Cap-Stripes.

Next I tried the original male and a different self colored female. She produced 15 babies, a variety of coat patterns, and several Cap-Stripes. I kept two Blaze Berkshires from this bunch, bred them, and got 4 Cap-Stripes from a litter of 9.

I kept a Cap-Striped male from this litter, bred him to a Cap-Striped female and again got an extremely small litter. This time there were only 5 in the litter, one still-born, and again, no Cap-Stripes.

My findings are that Cap-Stripe/non Cap-Stripe or non Cap-Stripe/non Cap-Stripe breeding produces normal to large litters with the Cap-Stripe patterning, but Cap-Stripe/Cap-Stripe breeding produces very small litters with stillborns and no Cap-Stripe patterning. My question is, could the Cap-Stripe patterning be lethal? Lorryta Bowker, CA

A Yes, it most definitely sounds like you have something here. Several people have now mentioned this tendency for Cap-Stripes to produce small litters with stillborns in them. Though we are not sure of the exact genetics behind Cap-Stripe, there seems to be good evidence that it is lethal. It would be very interesting to hear from other people who are working on this pattern. *

Updated October 29, 2018