A system of complementary genes in hybrids between Drosophila koepferae and D. buzzatii: a Markov chain model allows to make inferences about their number and relationships

In backcrosses between D. koepferae and D. buzzatii, the disruption of a system of species-specific complementary factors brings about hybrid male inviability. This system consists of a lethal factor, hmi-1, linked to the X chromosome of D. koepferae, and several conspecific autosomal suppressors. However, hmi-1 hybrid males can also be rescued by factors present in some strains of D. buzzatii. The present work aims to estimate the number of hmi-1 suppressors in one of these strains by means of Markov chains. The obtained results allow discarding models with one or more chromosomes having independent suppressor effect. On the other hand, models having n chromosomes that interact in groups of r, being 1 < r < or = n, to produce rescue effect, provide good approximations to the observed results. The best fit to the data is obtained with four or five chromosomes with suppressor effect, interacting epistatically in groups of three to rescue the viability of hmi-1 males.