I'm not sure which article, if any, that quote came from, but from knowledge of genetics I can tell you that any trait with something called full penetrance cannot be both accumulative and suddenly show up "strongly" in a family line as a surprise kit with bad malo. The term "gene penetrance" refers to how closely an organism's phenotype (what you actually see in the chinchilla) reflects its genotype (what you SHOULD see in the chinchilla given its genes). An "accumulative" or an "additive" trait is a trait that is affected by many different genes whose total effects get worse the more of those genes you have. For example, from what I know about the ebony trait, it could either be additive since the more "ebony" genes (which are at different locations on your chromosomes) that a chinchilla has, the darker the chinchilla is OR (more likely) the ebony gene has varying penetrance so that although a chinchilla may have the ebony dominant gene, it may still show some gray/white because the ebony trait is not fully expressed in that particular chinchilla. We wouldn't know which was which unless someone actually took the time and the money to look at an ebony chinchilla's genes in a lab.
So, if the malo trait is an "accumulative" gene, then there are a number of different genes that cumulatively affect how bad the malo is in the chinchilla. If malo is additive and both parents have malo, statistically it is more likely that they have malo from different genes, and if their kits inherit both of those bad malo genes then the kit's malo would be worse than the parents' because they have a "double whammy" of bad genes. Usually, you start with one or two bad genes, and as successive generations of malo afflicted chins have kits, you have more and more bad genes in the kits and they in-turn have worse malo. BUT you would not have malo show up randomly in a kit.
The only way that you would have malo show up totally randomly is if the malo genes have a lower degree of penetrance, so that there are a number of chinchillas wandering around with "bad" malo genes but don't have malo. Then, of course, in a kit the malo trait may suddenly seem to "appear" because the kit will express the malo trait that its parents had the genes for, but did not express.
Genetically, I would hedge my bets that the malo gene is actually dominant, additive, and partially penetrant. A recessive trait - unless it is very very rare - should show up in at least one kit about every other generation in a family line. It would be dominant, which means that all of the chinchillas that have that trait have the ABILITY to express malo, but not fully penetrant meaning that some chinchillas that have the malo trait just just randomly might not actually have malo (probably due to an entirely different factor like the chinchilla's environment). That is what you would call being "genetically pre-disposed" to malo.
Ok - whew - that was a mouthful. :hmm: Yea for genetics!
