Since I know nothing about genetics I can have the fun of making up theories all on my own. So here’s a little insta-theory
Let’s assume that genes give rise to traits; so for example you might have a gene for shy, or a gene or sociable, or gene for a strong immune systems. Now let’s assume that genes can migrate from one place in the genome to another. Now let’s assume that gene that are physically close to each other in the genome are more likely to be transmitted together while those far appart are more likely not to be transmitted to the next the generation.
Let’s say there is some advantage to having two traits at the same time. For example if you highly sociable then it might be good to have a strong immune system. Or alternately there is some disadvantages so for example if your shy you may not get much benefit from paying the expense of a strong immune system.
So, it seems reasonable that selection pressures would cause genes for particular traits to migrate into a physical ordering that sorts out the cost/benefits of their being inherited together.
I’m unhappy that this becomes a weak argument for prejudicial behavior.