Compatible vs. Incompatible

Here is what a normal set of chromosomes looks like... in an embryo resulting from a compatible cross (i.e., no CI).

But in an embryo resulting from an incompatible cross (i.e., a CI mating), the paternal chromosomes become abnormally heterochromatic, forming a ‘chromosomal clump.’

The ‘clump’ fails to form chromosomes, leading to developmental arrest (death) of diploid host organisms

(e.g., mosquitoes).

In haplo-diploid insects, the loss of paternal chromosomes due to CI is not lethal, but leads to all-male broods.