What if you don’t know which allele is mutant? For example, what if you’re presented with two true-breeding frogs: one that is gold and one that is yellow. If you don’t know what the predominant colour in nature is you can’t know which one is mutant. If you crossed them and all the progeny are gold, then you know the dominant allele encodes a protein to make it gold. The recessive, therefore, is “yellow” and you should name the gene “y” after the recessive phenotype. This means the dominant allele would be “Y”. Your offspring would therefore be Yy and the gold parent would be YY. The yellow parent would be yy.
Figure 2 from the Appendix shows purple and white flowers. . If we note the genotypes, we can see that the het (middle) shows the same colour as the purple parent; thus purple is dominant. "Albino" is a good name for the white mutant phenotype, so let's call the recessive allele a.
This means that the wild-type allele, which is dominant, would be indicated as A.
This means that the gene NAME is albino, and in our system there are two alleles for the albino gene; the mutant allele, causing albinism, and the wild-type, which allows normal colour.