No - it doesn't work that way. In fact, the mice don't work that way either
You are right about black tending to be dominant over many other colors in mice but it's nothing to do with it being a darker color. It's just a 'dominant' gene. I'll explain using the shorthair/longhair trait if you like.
The basics first...
DNA is a molecule that codes for an organism. It's like a 'blueprint'. Genes are lengths of DNA that code for specific characteristics. For example, a gene can control eye color or coat color.
Chromosomes are basicaly just DNA so they are made up of genes. When two animals mate, their offspring get half their chromosomes from one parent and half from the other. They are paired as well - so one of each pair comes from each parent in the end. In the majority of fish and mammals, chromosomes also determine sex.
There are two particular chromosomes - the X and Y - that are responsible for this. Males always have an X and a Y and females always have two Xs. So I have two X chromosomes (XX). As you get one chromosome from each parent, the father always determines sex. To perhaps clarify this a bit: As a female, I've inherited an X from my mother and an X from my father. My mother (XX) only had Xs to give me - my father (XY) could have given me a Y instead though. Had that been the case, I'd have one X and one Y (so I'd be male). The chances of being male or female are therefore 50% and your dad's responsible
Ok so my point is that you get half your chromosomes from each parent so you also get half your genes from each parent. You have to keep in mind that chromosomes exist in pairs so you also have two of each gene (each from each parent). Different forms of a gene are called 'alleles'. For example, a gene that controls eye color may have one allele that produces blue eyes and one allele that produces brown (contrary to popular belief, this isn't the case in humans - eye color isn't actually a simply Mendelian thing like this).
Now back to the mice: A wild mouse has only the alleles coding for short hair (as longhair is a mutation that occured after domestication). So it has two shorthair alleles (that can be represented as SS). Longhair mice must have two longhair alleles to be longhairs (ss). HOWEVER, if you were to cross these two hypothetical mice, all their offspring would be shorthairs. Now this is because their offspring would inherit one shorthair allele from the wild mouse and one longhair allele from the domestic mouse (Ss). As shorthair is dominant to longhair, all the mice would be shorthair but they'd be
carrying the longhair allele 'hidden' as well.
Now if you crossed these mice, you'd get both longhair and shorthair offspring because some babies would inherit only longhair alleles (and be longhairs - ss) or only shorthair alleles (and be shorthairs - SS) or they'd inherit one of each (and would still be shorthair because shorthair is dominant over longhair - Ss).
I actually taught myself genetics when I was younger because I had lots of cats in the neighbourhood and I wondered whether I could predict what colors they turned out - but I digress
What I wanted to emphasize is that the brightness/darkness of a color is not connected to whether it is controlled by a dominant or recessive trait. In cats, white is dominant to black (indeed, dominant to
any other color). There are also what are called 'modifier' genes that simply modify the basic coat color. There are lots of these in guppies but the easier example is in cats (or mice). For example, a black cat that also has two copies of a certain modifier allele will appear blue (grey) instead of black even though it is geneticaly black. So not all colors are controlled by a single gene anyway. Very few, in fact, are that basic.
As for the mother or father having more influence on offspring color - in mice this is almost definitely purely coincidental. In guppies, however, a lot of genes that code for color are X or Y linked (which means the genes are on either the X or Y chromosome) so offspring really are affected by which parent was a particular color. If a particular gene is Y-linked, it means you can only ever inherit that from your father and you must be male to get it (as you become male if you inherit a Y chromosome
).
Anyway - I agree that you don't need to know all about genetics to breed nice fish. But especialy with things like guppies that have lots and lots of variations, it does really help. In particular, if you're looking to develop a new strain or breed 'show' guppies, you need to know what the outcome of a cross will be to save time (and money!) and to make sure you don't completely change the color, for example, in a line that you were simply trying to improve the fins of or something like that. But it's always fun to experiment and try to work things out yourself. After all, most of the stuff we do know about guppy genetics were worked out just like this - through breeding experiments.
BTW, when I was talking about complexity, I didn't mean that understanding genetics is difficult. If you take the time, it gets easy quite quickly (though, obviously, you need to be interested in it first). The reason I mentioned that was because I wanted to point out that, actually, absolutely all the genetics guppy breeders (or any other 'breeders'
) use are over-simplified versions of what really happens. Genes, in reality, are activated by other genes, which are controlled by yet others and so on
It's not just a matter of 'this gene gives you black scales' and 'this one makes you albino'
