Genetics
Whether you understand genetics or not, when breeding rats it is very important to know the basics.
Almost all of a rats' traits, like those relating to behavior, health and the way it looks, are coded for in it's DNA. DNA molecules are long strands of connected molecules called nucleotides that together make up a genetic code. Our DNA molecules contain genes and other sorts of genetic information. In our cell cores (or "nucleus") They are packed with associated proteins into structures called chromosomes. We have 46 such chromosomes, 23 from mom and 23 from dad. Brown rats, Rattus norvegicus, have a few less, 42 - which also contains one set from mom and one from dad. Each set contains roughly the same genes. This means that a rat has two of most genes. Genes sometime come in different versions, different varieties. DNA changes (mutates) sometimes, for example during production of sperm or egg cells or as the result of outside disturbance such as high gamma radiation or chemical carcinogens like formaldehyde. Different variations for a gene can give different expressions. For example, a gene for fur coat colour can come in two (or more) varieties, brown and black. Because a rat can have two of each gene, one on each set, it can have the black version of the fur coat gene on the chromosome set inherited from mom and the black version on the set inherited from dad. Different versions of a gene are called alleles. AA = Agouti (wild type) Aa = Agouti carrying a non-agouti gene aa= non-agouti (black) Agouti is Dominant, Black is Recessive. Two genetically AA (Agouti-based) rats will only ever produce more Agouti based babies. (AA x AA = all AA) The same with one AA (Agouti) and one Aa (Agouti carrying non-agouti). (AA x Aa = 50% AA, 50% Aa) But two Aa (Agouti's), or one Aa (Agouti carrying non-agouti) and one aa (Black) will produce a litter with both Agouti and Black-based babies in it. (AA x Aa = 50% AA, 50% Aa) Two aa (Blacks) together will create an all black-based litter. (aa x aa = all aa) The trick is knowing what your rat is genetically (which if they are Agouti based, there's no way of knowing whether they're AA or Aa unless you know that one of their parents was black-based (therefore passing on a little 'a') or you've bred them before and figured it out from there). As a baby randomly gets two genes from each parent. Ex. AA (Agouti) x Aa = approx half AA and half Aa (agouti) babies. AA x aa = All Aa babies. Aa x Aa= 1/4 AA, 1/2 Aa, 1/4 aa. etc. See Punnet Squares if you don't understand how this was worked out. Now, most dilute colours are recessive as well, and therefore act the same way as black does. Mink, Blue, Ruby-eyes, and Pink-eyes are all recessive dilutes. Chocolate on the other hand is either dominant or co-dominant. Meaning that a Chocolate rat with only one Choc alleles present will be 'lighter' then a Chocolate rat with both alleles present. The same goes with the coat type PowderPuff, if a rat only carries one PowderPuff allele, its is half way between PowderPuff and Standard, called a Puff. |
|