The English Spotting, or Broken, gene creates a more or less random pattern of white spots or patches over the rabbit's color. Usually, the patterns are very smooth-edged. There are only two genes in this color group: En and en.
En: BROKEN PATTERN
En is always dominant over en. Any rabbit with one copy of the En gene will automatically be broken-patterned. The colored portions of the fur are patched or blanketed with white in between. Ideally, a broken patterned rabbit should have a balanced marking on its nose (known as a butterfly), the ears should be fully colored, the front feet should be white, and the colored portion should be more than 10% but not exceed more than 50% coverage.
This gene has partial dominance- it is ALWAYS expressed if present. Rabbit cannot “carry” the broken gene- they are either broken, or not. Two solid rabbits CANNOT produce a broken rabbit.
This gene also affects the ej (harlequin) gene, turning the banded pattern into a spotted pattern (usually called tri-colored or, in the case of a magpie, piebald or broken magpie).
en: NO BROKEN GENE
Rabbits without the En gene will not display the broken coat patterns.
"Charlie" is the term for a rabbit with less than 10% color. There are two types of Charlies- genetic Charlies (EnEn) and false Charlies (Enen but with less than 10% color- technically just a poorly patterned broken). True genetic Charlies (En) typically lack nose spots. Genetic Charlies (EnEn) will only ever be able to contribute an En gene, so will always pass on one copy of the gene to their offspring, resulting in always broken-patterned kits. There is some belief that Charlies may be more prone to digestive issues such as megacolon. Charlies are also not recognized in many breeds. However, they can be useful to a breeding program- if you are willing to wait for a second generation, the resulting Charlies could be bred with a solid-colored rabbit, resulting in all brokens. I've heard that the term "Charlie" comes from Charlie Chaplin, because the abbreviated butterfly (nose marking) that most Charlies have.
REW RABBITS (cc) AND THE BROKEN GENE
Because the REW (Ruby Eyed White) gene (cc) masks all color and pattern, it's impossible to tell by just looking at a REW rabbit whether it is a solid (enen), broken (Enen), or Charlie (EnEn). You may be able to determine whether the rabbit expresses the En gene by the pedigree/parents, but otherwise the best way to determine is to test breed to a solid (enen) rabbit and test breed.
OTHER WHITE-MARKING GENES
There are other genes that can cause white spots or white markings on a solid rabbit that are NOT the broken gene such as the Dutch gene (Du) and the Vienna gene (V).