"It means that the two genes responsible for albinism reside at different locations and do not line up to create a homozygous recessive. Look at it this way:



The albino Ruthvens is:



aa BB



and the albino nelsons is:



AA bb



The offspring would inherit a dominant and a recessive from each parent making them:



Aa Bb - technically making the neonates double het."





I guess this is where I am having a mental block. Why should the genes particular location on some chromosome matter? Lets say the particular gene responsible for albino is both species is tyrosinase. Albino nelsons are homo tt and albino ruthvens are also homo tt, regardless of where the genes are located. So, if you cross them the nelsons parent contributes a tyrosinase null allele (t) and the ruthvens contributes a tyrosinase null allele (t), so the offspring inherit two null alleles (tt). Where is the functioning copy of the gene coming from? In my mind I can only resolve this if two different genes are responsible for albino in each species (but I am totally open to being convinced I dont know what the hell I am talking about).



I think in your example A and B would be different genes not just different locations on some chromosome for the same gene in different species.



Best,

Vinny
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“There is a grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that whilst this planet has gone on cycling according to the fixed laws of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” -C. Darwin, 1859



Natural Selection Reptiles

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