Complex sentence: A social chromosome is present in the red imported fire ant; this chromosome can differentiate the social organisation of a colony, where it carries one of two variants of a "supergene" (B and Bb) which contains more than 600 genes.
Split into simpler sentences: A social chromosome is present in the red imported fire ant. This chromosome can differentiate the social organisation of a colony carrying one of two variants of a "supergene" (B and Bb) which contains more than 600 genes.