This time to make things a bit more ratty, I thought I'd use some of our pictures. If pure-bred self rats are bred together, you get self babies. Pure-bred huskies always give huskies. Again, I'm stating the obvious.

Things get harder when we consider the case of breeding a pure-bred self to a husky. As usual, the babies will inherit information from each parent. However, it is clear from the photo that Junior despite carrying both self and husky genes, only the self one is showing. The self gene is said to be dominant and the husky gene is said to be recessive.

This last point is not as trivial as it looks. What do you get if to you get if you cross a pink-eyed white (PEW) rat and a true-breeding black rat together? The babies will carry white and black in its genes, but that doesn't mean we will get grey rats. Logically, the babies can't be grey or any other colour than black or white, because black or white is the only information available. As it turns out, PEW is recessive so the babies will all be black.

This point is obvious for husky or not husky, and for dumbo or not dumbo, but people sometimes don't realise this fact can also apply to colours. Complete dominance doesn't allow for an "in-between" state of affairs. In the PEW case above, we could as easily refer to the whiteness as the albino gene. The babies are either albino or not albino.

In the example above I mentioned breeding a pure-bred self to a husky. The litter were all selves, not a single husky.

So be careful. The genes of rats showing a recessive characteristic are easy to work out. However, rats that show a dominant characteristic could be true-breeding or carry the recessive gene.

This way of describing genotypes is long winded and some kind of shorthand is needed. This becomes more important when you are describing more than one gene.

When looking at one particular characteristic, rats inherit one gene from mum and one from dad. Different genes are represented by different letters of the alphabet, usually the initial of the characteristic it represents. Capital letters are used for dominant genes, lower case letters are used for recessive genes.

There are commonly used letters for commonly discussed genes. It doesn't really matter which letter you use as long as everyone understands each other. Usually the name of the gene is named after the characteristic it is responsible for. The named characteristics are often recessive, but not always. There isn't one I'm aware of for the roaning effect on huskies, so I am going to use the letter Q.

Rats with recessive characteristics as the name suggests are less likely to occur from random breeding. As such, there tends to be less of them. Rats showing a recessive characteristic are likely to be outnumbered by those showing the dominant characteristic (which will be a mix of true-breds and carriers). So with our new notation, let's explain those genotypes again...

Now that we have identified three genotypes, that gives us six possible ways that a litter could come about. We'll cover that on the next page.