system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the science behind Children who's parents are closely related end up being born with birth defects?

I really have no good reason to ask this other than i saw a article on king tuts birth defects and the fact that his parents were most likely brother and sister.
gpt
in order for recessive traits to be expressed (to show up), you need to have two of them; otherwise the dominant trait will be expressed. when parents are closely related, they are more likely to have the same recessive traits, increasing the likelihood that their offspring will inherit two of them. since defects are often recessive, they tend to appear more frequently in the offspring of closely related parents. 

the moral of the story is that genetic diversity is good!