What would determine the rate that a hereditary condition reveals itself after years of dormancy?

Question

Long ago, an Eldritch deity was summoned to the city of Innsmouth within a ritual circle, where it was killed and consumed by the population. Devouring the flesh of the deity increased the mana supply of the individuals to astronomical levels, strengthening their arcane abilities. As the population grew in power, the prestige of Inssmouth increased in the world. As all inhabitants benefited from their mana supply increase, the city became known as a center for magecraft where the most powerful mages were located. This lasted for a period of 500 years, as the population passed down their arcane power to their descendants.

However, over time, problems started developing in the city within the past 50 years. The current population began suffering from defects and mutations.It turns out that the increase in mana from the god began to mutate future generations. Individuals with heavy deformities became twisted and inhuman, as their mental faculties decreased while becoming animalistic. More defects in the gene pool began showing up as a significant portion of the population gave birth o monsters. Ultimately, this ended with the entire city becoming filled with debased creatures with no semblance to humanity.

Somehow killing and consuming the pieces from the god had an effect on the genes of the population. This hereditary illness was passed down to their descendants, but didn't reveal itself. The chaos of the mutations occurred suddenly and quickly after centuries of stability. What would cause this massively delayed reaction?

Answer 1

It looks like you are seeing for the transition from a genotype (where the changes in DNA are in the genes but don't necessarily express themselves) to a phenotype (where these same genes give rise to the monsters)

This is most easily explained through a new gene expression where the existing genes suddenly start producing certain proteins that lead to the mutations.

There are many ways to regulate gene expression and many of these are very subtle. For a gene to stay dormant for 450 years and then suddenly express itself through the entire population you'd expect that something in the environment is to blame, otherwise you'd see it after x generation instead of years, or only in a sub-population that mixes with another group.

As your world has magic this is probably the easiest explanation. Did someone else attempt to summon the god? Did someone do a ritual sacrificing members the race? Did a new kind of spell come into vogue? Did they find a certain crystal that ups your mana pool if snorted?

For a real-life example: in the 1950's a new medicine was marketed to help with a wide range of issues, including anxiety and morning sickness, and actually helped against those things! Amazing stuff. However this drug also interferes with a protein called SALL4 which, while not that important in adults, is vital in unborn babies for the proper growth of limbs and other structures. In the end over 10.000 children were born with deformities, a lot of them perishing shortly after birth from the effects.

Answer 2

Mana magnet.

God power is heritable, as you establish in OP. Mana can cause mutations; also in OP. The god power grants mana but also serves as a long term mana attractor or sink. Subsequent generations in this town have more power than their ancestors thanks to this god meat effect.

The increase gets to a point where it is too much for biology to handle and things start to break. That is where you are. Mostly this makes degenerate monsters.

0.1% of these mutants will not be monsters, but new gods. When the new god comes into its own, it will be hungry. The degenerate monsters will be happy to feed it with their own flesh, and that of any of their less willing mana-rich relatives they can catch and bring with to the coming of age ceremony.

This event is what the Foundation (working thru the federal government) was trying to avoid, to no avail. Fallback plan: the best way to fight a god is with another god. They have an Innsmouth child with potential whom they are trying to raise as fast as they can, on a diet of mana-rich god meat from various sources.

Answer 3

Natural Selection

The same genes that manage Mana capacity are the same genes that cause monster mutation. if enough genes are activated at the same time of course. The initial Devouring gave different mutations to all the families.

The increased mana combined with the new magecraft prestige caused mage families to arise and political marriages or marriages for power between mages ensued. Fast forward many generations and enough genes have been activated in any individual that almost any combination between members is resulting in monstrous creations.

450 years is about 10-15 generations. Assuming the most powerful mages married amongst themselves to produce the best possible offspring (and highest mana pools 100% precisely and unique gene combinations), for 10 generations you could assume 2^10 gene applications or 1024 unique genes that are a mana mutation (32,768 for 15 generations). Likely though, pairings would duplicate potential gene combinations meaning this is an upper bound.

So monsterification happens after a number of combined gene mutations occur. Let's say it only occurs after 666 god gene mutations which could easily occur within your 10-15 generational gap and once the genes are that widespread almost everyone should have a high combination of genes that could create monsters.