W-series, or Dominant Spotting.

W-locus

W-series genes within the mouse fancy include W, W^sh and W^bd. There are quite likely some other forms of W around, like W^v, viable dominant spotting.

1. Dominant white spotting W

The dominant white spotting gene W is responsible for Variegated (and possibly one of the newer varieties, Berkshire). Genetics know the gene as "kit oncogene W" or KitW and there are several mutations of it. This gene is also called lethal white spotting, because the combination W/W is lethal. These mice are black eyed whites, anemic and die before two weeks of age. The main effect of this gene is small, ragged edged splashes of colour on a white background. Unlike the name implies, W isn't truly dominant, but semidominant. This means that a W/w (or to put it correctly, W/+) mouse can be Variegated - but it can also be non-marked, or even completely white. W is a tricky gene to work with, it may act as a recessive and may not always produce spotted mice.

This variety is also highly dependent on modifiers, which may be part of the k complex. Just like the Even and Broken marked, the Variegated mouse takes a lot of patience - and mice - to breed into perfection.

2.1. Interaction between W and s

When a mouse has both W^w/* and s/s, it is either entirely white with black eyes or has small pigmented areas in the region of the ears and/or the haunches.

Black variegated, a/a B/* W/w pic: Anniina Tuura

Black tan banded, at/at B/* Wsh/w pic: Arttu Väisälä

Black capped, a/a B/* Wbd/Wsh pic: Arttu Väisälä

2. W^sh, Banded

The major banding gene mouse fanciers work with is actually gene called "sash", not "banded". The latter does exist and is deal with in the next chapter. The Banded gene sash, W^sh, is rather new to the mouse fancy. It was first reported in a lab (it was a spontaneous mutation) in 1978 and in the 1980's it was introduced to the mouse fancy. This dominant gene produces a white band around the mouse's waist. When heterozygous, the mouse has this typical banded appearance, which can vary from tiny trace of white to huge wide band. When homozygous, the band widens to leave colour only in the head and rump. These latter kind of mice can be selectively bred to lose all pigment into black eyed whites. Banded is easy to introduce into new colours and coat types as such, but of course it will need a lot of selective breeding to get into perfection. Other marked genes are a big no-no for banded breeding, especially minor genes causing tail and head spots.

When breeding Bandeds, one should never mix in other marked variety genes. White spotting genes are an especially unwanted lot, as well as minor genes causing head and tail spots.

3. W^bd, Capped

The mouse variety Capped may simply be something you can breed out of your ordinary everyday Bandeds. On the othar hand, it may also be the result of a specific gene. The following is my theory on the subject, backed by more than a decade of breeding Cappeds, as well as what genetics say about the effects of the banded gene and interaction between sash & banded. The descriptions available in scientific sources fit quite well my own findings. The major difference between sash and banded mice (both homozygotes and heterozygotes) is the amount of white on W^bd mice and the fact that there are always anaemic young in capped litters (which does not occur with W^sh mice).

Banded is a semidominant gene, causing variable phenotypes. With Capped x Capped matings, the litter size is usually somewhat smaller than with other varieties and the number of young reaching adulthood noticeably smaller. Some of the young are aneamic and some of them perish around 2-5 weeks of age. Those who survive, grow up to be perfectly normal mice. The whiter the young, the more likely it is to perish.