Linkage relationships and haplotype variation of the major histocompatibility complex class I A genes in the cichlid fish Oreochromis niloticus

The haplochromine cichlid species flocks of the East African Great Lakes ar e one of the best examples of adaptive radiation. Analysis of genetic varia tion among these species provides valuable information on species relations hips and timing of speciation events. Although the haplochromine cichlids g enerally display little genetic variation, the major histocompatibility com plex (Mhc) genes have been found to be highly variable. A study of the link age relationships of the Mhc class I A genes in the cichlid fish Oreochromi s niloticus was therefore undertaken. Class I loci were identified, and the ir segregation in seven mothers and their haploid embryos was determined. I n total, 56 class I A sequences were found among the seven families. A stro ng concordance of segregation was observed in five haplotypes among the emb ryos, indicating a close linkage of all loci. The number of loci per haplot ype varied from 11 to 17, while the: total number of distinct loci found am ong all families was 22. These findings show that all class I A loci are li nked in a single genetic cluster in O. niloticus.