6. am - Mottled Agouti

The mottled agouti gene is a result of radiation experiments at Oak Ridge. It uncertain whether this gene is available for mouse fancier and if it is, where. (The author welcomes your feedback!) On the a-locus, am is lower than at and higher than a.

Like the viable yellow Avy, mottled agouti gives widely varying phenotypes ranging from deep black, completely tanless mice that can't be told apart from extreme non-agouti ae/ae mice, through variable mottling of yellow/red and black to pseudoagouti (full agouti pattern). Again, like Avy, the phenotype variation of the young is strongly influenced by the agouti locus genotype of the mother. Both homozygotes and heterozygotes with a (am/a) show variance in coloration.

It is quite interesting, that the two a-locus motting genes, Avy and am can produce almost all possible a-locus derived phenotypes between the two genes, with pseudoagouti being the "common end": Avy produces colours from all red through mottling to pseudoagouti, am produces colours from pseudoagouti to extreme black. As both genes can produce pseudoagouti, only breeding tests can show whether a pseudoagouti mouse is a Avy or a am mouse. Of course, Ahvy can produce the whole of variation all by itself!

6.1. Homozygous Forms

As has been noted above, the phenotype of am/am can vary greatly. For a fancier, am can be useful in breeding a line of brindles, blacks and dilutions of these two varieties.

4.2. Heterozygous Forms

When am is heterozygous with any of the a-locus genes higher on the dominance scale, it does not show. Therefore, only useful heterozygous forms are am/a and am/ae. These, however, have the same phenotype as homozygous am/ am.