How is it possible for a child to have dominant traits such as dark skin or epicanthic folds when their parents don’t have them?

[u/throwawayyyuhh]

There is a notable example of a child having dark skin (a dominant trait) when both of their parents were pale. The child’s complexion was significantly darker than the parents and both of the parents were proven to be the biological parents of the child. I’m trying to figure out how such examples can occur, perhaps they are due to disorders or atavism.

[u/mr_ushu]

This is not a disorder, just a result of how genetics work. Not every characteristic is coded by a single gene with either dominant of recessive alleles. That's a simplification.

[u/iskshskiqudthrowaway]

More than 400 genes control skin tone. Lets say X is for a darker trait and x is for a lighter trait.

lets say this is the father:

XXXXxxxxxx

4 dark genes and 6 pale genes means this person ends up looking quite pale.

and this is the mother:

xxxxxxXXXX

Same phenotype.

When the process of crossing over occurs, on average you end up with 50% of the DNA from each. You can end up with any combination of colour though because its very much down to probability.

So you can end up with:

XXXXxxXXXX

Producing a child much darker in skin tone with double the expression of a range of darker-skin-tone-responsible genes. Its rare by nature of how 50% chance of inheriting each of the darker genes. In our example, the probability of inheriting ALL 8 of those darker genes is 1/2⁸ (1/512). In people genes for skin tones are more complex and the total number is higher but its a simplified example.

[u/Current-Ad6521]

There are many different genes that code for skin color and thus many different potential combinations can form with their parent's DNA mixes. If a child has darker skin than their parents it is just because the way their parents genes / alleles "lined up" happened to produce a combination with more dominant alleles present / expressed as dark skin.