When her head game is so strong, she sucks the chromosome right out of you.
Chromosome Sucking Oral Sex
Explanation
The joke plays on the idea of someone being extremely good at oral sex, so good that it's as if they are physically extracting something from the other person, in this case, a chromosome. It uses hyperbole to create humor. It's also a dark joke due to the idea of retardation being linked to missing chromosomes.