The gene for the broken color is Enen.
The solid gene is enen. As long as there's no color "broken up", over a white background, the rabbit is not a broken, its a solid.
Each broken colored rabbit "carries", the solid gene, which is (en).
When you breed a solid to a solid, you will get 100% solids, because it's the most recessive gene in the series. Each parent only has an (en), to give to its offspring, so all babies are enen solid, like the parents.
When you breed a broken to a solid, in theory you should get 50% brokens and 50% solids. The broken parent has an (En), or (en), gene to give to the babies, whereas the solid parent only has (en), to give to the kits.
When you breed a broken patterned rabbit to another broken, they will have a 25% chance of producing solid, a 50% of producing broken, and a 25% chance of producing a charlie.
What a Charlie is:
A charlie has the EnEn gene. It's basically a broken patterned broken. Charlies often cannot be shown because most of the time they have too little amount of color.
When bred to a solid, a charlie will only produce Enen brokens, because the Charlie only has the (En) gene to give, and the solid only has the (en) gene to give. You can only tell your rabbit is a true, genetic Charlie if you breed the rabbit in question and it ONLY produces all brokens. Usually a minimum of three tries is needed, because sometimes an Enen broken can also produce all brokens with a solid pairing. However, it would be VERY strange if a correct broken produced all brokens 3 times in a row!
What some people THINK a Charlie is:
Some people think a Charlie is just any rabbit that has not enough color to be shown. A rabbit needs to have over 10% color, in the judge's opinion, to be shown. If it has less then 10% color, it will be disqualified. A Charlie is not actually a rabbit that has too little color; it's a rabbit that has two broken parents and can only produce brokens when bred to a solid. Thus, in the rabbit world, a true Charlie is usually referred to as a "Genetic" Charlie.
How do I know my Holland Lop has enough color to be shown?
I'll include this question in this blog just because it kind of fits the with the theme.
Usually, if the Holland has color over both ears, on the nose, around both eyes, and a little bit on its back that's enough to allow it to be shown. If it has no face markings it cannot be shown. If it has no body markings, but has severe face markings, it can be shown.
The little guy below is very sparsely marked with his black tort, yet he has enough color to be shown. At a younger age he only had the face markings and a single stripe down his back. As he molted his baby coat and matured, he grew extra spots and more color.