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Genetics the Simple Way

When you are breeding mice it helps to have a grounding in genetics. Many breeders I have met tell me that genetics sounds confusing and that they do not know much about it, however when they talk about which mice they would breed together to achieve certain coloured or patterned offspring, they prove that they do know. Although they do not call it genetics, these people know, for example, which genes are dominant because they know that mice with a certain dominant marking will pass it on to most or all of their pups even without the other parent having the same marking. And it's that simple. It is basically just learning what is dominant and what is recessive to achieve the result you are aiming for.

Piglet, a PEW fuzzy buck. This gene is recessive

The topic of genetics can be extensive, so I will just give a simple example here and then link to some other more detailed pages.

Let's say we have a satin mouse and a normal coated mouse, both cream. Satin coat is recessive, meaning that if another more dominant gene is present that it will 'overrule' it in the resulting offspring. Let's give normal coat the symbol S and satin coat the symbol s. For the purpose of this example we will asume that each mouse possesses one instruction for coat type from each parent, and that in this case both of our prospective parents' genes are homozygous (the same). That means:

Normal coat mouse: SS

Satin coat mouse: ss

All we do now is to work out all the possible combinations of the genes - remembering there must always be one from each parent. So, the combinations from this pairing are:





This means that all the offspring would have normal coats but would all be carrying the satin gene. Because they are carrying the satin gene this means that the possibility exists for their offspring to have satin coats. For example, we will 'mate' a brother and sister from the above litter who are Ss and Ss and get:





This means that the first example would have a normal coat and not carry the satin gene at all. The second and third examples would have normal coats but carry the satin gene and the fourth example would have a satin coat. Because mice usually have more than four pups in a litter, the working out above will give a rough percentage showing that 25% of the litter would have satin coats - i.e. if the mouse had a litter of twelve then three would have satin coats.


To find out what colours and markings are dominant, along with other genetic information, I would suggest referring to books and other web pages. I have included some links below to sites that I find both helpful and interesting, some of which cover genetics extensively. If you know of any other helpful genetics pages you think I should link to, please email me.

Finnmouse's Genetics Page - Brilliant! If you look at only one page to learn about genetics, this is the one to go for.

Eva's Mouse Varieties Page

Genetics page based on Finnmouse's page with nice photos (even if they are not all good examples of the varieties they illustrate)

A scientific site, but interesting for those 'into' genetics ...

Rats and Mice - the mouse genetics 'bit'

Jackson Laboratories - various information about lots of mouse related things, including reams on genetics

Rodentfancy.com - genetics section

Mouse Genetics

Mousedo Mousery - explanation of various genes in mice

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