Shields and Procunier (1982) described four sibling species of the Simulium arcticum complex in Alaska, and Procunier (1984) described a fifth in western Canada based on possession of unique
paracentric inversions in Y chromosomes.
Crossovers within the loops of both pericentric and
paracentric inversions result in chromatids with duplications and deficiencies.
This chromosome has been shown to be polymorphic for up to six
paracentric inversions (Ruiz et al.
There is a long history of theoretical models and empirical tests dealing with the relationship between inversion length and the processes generating and maintaining
paracentric inversions in the Drosophila genus.
White (1978) observed that in over 300 species of Drosophila,
paracentric inversions were 200 times more common than pericentric.
They owe their prevalence in part to two biological peculiarities of Drosophila that minimize the harmful effects of crossing-over within a
paracentric inversion loop.