A recombination survey using microsatellites: the O chromosome of Drosophila subobscura.

Recombination plays an important role in species adaptation since it acts as an evolutionary force that can influence genome pattern organization. However, recombination can be detrimental in some situations, causing the breakdown of some adaptive gene combinations such as coadapted gene complexes. Genetic and cytological chromosome maps allow recombination throughout the genome to be analyzed. In this study we compare the recombination rate of two types of homokaryotypic lines of D. subobscura (O(ST) and O( 3+4 )) using a set of at least 13 microsatellite loci. The genetic maps obtained present similar lengths: 184 and 196 cM for O(ST) and O( 3+4 ) chromosomes, respectively. For most pairs of markers analyzed, a sample size of about 150 individuals appeared sufficient to obtain appropriate recombination values, with the exception of markers located in the same cytological band. Recombination rates seemed to be fairly uniform along the O chromosome, but some regional differences were observed. Several recombination hot and coldspots were detected, and their numbers were different in the homokaryotypic line types (O(ST) and O( 3+4 )). This variability could be attributed to differences between the genetic content of the two arrangements or to differences between the lines.