This article is from the Winter 2001 AFRMA Rat & Mouse Tales news-magazine.

By Nichole Royer

Dawn R. G. Martin, Rochester High School, MI, e-mail
QAfter reading over your page, I have decided that you are the type of person who is well enough acquainted with rats, genetics, breeding, and intelligence that I am looking for. I am a sophomore at Rochester High School in Michigan and am currently going over genetics in Biology. Our assignment is to choose two of the six rats (three males, three females) to breed to try to create a Siamese with Dumbo ears. The coloration of the rats are as follows: A) male Siamese with blaze, B) male Fawn with Dumbo ears, C) male black and white, D) female Siamese rat, E) female black and white, F) female Black. According to the accounts that I have read, the only way to breed a Siamese rat is if the two Siamese rats are bred. I have also heard that you can breed a Siamese with a black rat. Then, all the F1 rats will be black but will carry the Siamese gene. Then, you can breed them back to their mother and theoretically, one-quarter of the litter will be Siamese. However, we do not have time to make F1 black rats and then breed them back to their mother. So, the only way that I can get Siamese rats without having to breed rats twice, is if I breed the two Siamese. But how would I get the trait of having Dumbo ears in their genetic code? The only rat that I know for sure has the Dumbo trait is the Fawn male. Yet, I have read that the Fawn gene is dominant to the Siamese gene. So, if I bred the Dumbo Fawn male with the Siamese, I may get a Dumbo rat, but not a Siamese one. So you see why I’m having troubles. Do you have any ideas, suggestions, or tips on how I can work around this problem? Is it possible to create a Dumbo Siamese from the options that I have been given or has my Bio teacher thrown out an unsolvable lab just to teach us about genetics and rats? Any information or help that you can give me is greatly appreciated. Thank you for your time.

AYour Biology teacher has given you an interesting puzzle. I have bred Siamese rats for many years and am knowledgeable about the Dumbo trait as well. With the information your teacher has given you I can tell you that there is no way to breed the rats you have to choose from and produce a Siamese Dumbo in the first generation, unless it happens by pure luck.

Both traits you are working with are recessive, thus both parents would have to carry both traits in order to produce a Dumbo Siamese. You do not have any rats to use that exhibit both traits. My first question to your instructor would be to ask about the background behind these six rats? What colors were their parents, and were any of them Dumbos? Without that information there would be no way to breed this group and know you were going to produce a Siamese Dumbo in the first generation.

I can tell you what you would likely get from breeding each combination. This is of course just based on the characteristics they are exhibiting. Most rats will have additional recessive characteristics that you know nothing about without knowing their background. Thus, other colors than what I mention may occur, but there is no way to predict them with the information provided.

• male Siamese with blaze X female Siamese rat = all Siamese babies, most of whom would have white markings (a disqualifying characteristic in show Siamese)
• male Siamese with blaze X female black and white = all black and white and possibly a few black selfs (no white)
• male Siamese with blaze X female black = some black and white and some black selfs
   
• male Fawn with Dumbo ears X female Siamese rat = all Agouti with normal ears
• male Fawn with Dumbo ears X female black and white = all agouti and white and possibly some agouti self, all with normal ears
• male Fawn with Dumbo ears X female black = all agouti with normal ears
   
• male black and white X female Siamese rat = all black and white and possibly some black selfs
• male black and white X female black and white = all black and white and possibly some black selfs
• male black and white X female black = all black and white and possibly some black selfs

As you can see, none of the combinations would produce what you want. I’d suggest asking about the rats’ backgrounds since more information may solve the puzzle.

I hope this has been of some help.

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