The chromosome number (2N) of walki

The chromosome number (2N) of walking catfish (C.macrocephalus) in Thailand is 58
(Donsakul and Magtoon 1989). Although the exact size of the genome is not known, the genetic map
of walking catfish may be quite large. A large number of genetic markers will be required to span the
genome evenly. Two types of genetic markers, microsatellite and AFLP are being developed for
construction of genetic map in a backcross family of hybrid catfish ((C. macrocephalus x C.
gariepinus) x C. gariepinus). Because of their high level of polymorphism, their relatively even
distribution throughout the genome, microsatellites and AFLPs are ideal markers for the construction
of highly resolution genetic maps (Vos et al. 1995; Kocher et al. 1998; Agresti et al. 2000; and
Waldbieser et al. 2001). Over the past decade, microsatellite markers have been extensively
characterized in various numbers of fish species. Microsatellite DNA is comprised of tandem repeats
of short, simple nucleotide sequences. The majority of microsatellite loci in fish genomes are
composed of the GT motifs, similar to that of higher vertebrates, e.g., rat and human. In addition,
microsatellite markers are often conserved among closely related species, e.g., salmonids and
cyprinids. Primer pairs for GT dinucleotide microsatellite loci of walking catfish are being developed
for population study and genetic mapping. In this study, primers of Clarias macrocephalus, C.
gariepinus, C. batrachus, and Pangasius hypophthalmus microsatellites were tested for PCR
amplification on the DNA of C. macrocephalus and C. gariepinus. Polymorphic microsatellite loci
were chosen for genotyping of individuals from a backcross family for mapping purposes.