Test of Mendelian segregation and linkage relationships among 69 microsatellite loci in rohu ( Labeo rohita)

Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneshwar, Odisha 751 002 IndiaKey words: Linkage, Mendelian segregation, MicrosatellitesIndian major carp, rohu (Labeo rohita) is an importantcultivable freshwater food fish species distributed throughoutSoutheast Asia. It contributes nearly half of total freshwateraquaculture production (0.57 mmt) in India. To meet the ever-increasing demand of fish food, augmentation of productionby developing high yielding and disease resistant breeds areimperative. This warrants use of modern technologies thatcan provide acceleration, reliability and sustainability toconventional breeding. The starting point may be developmentof genetic markers and placing them in linkage groups leadingto generation of gene maps to assist in tagging of trait genesor loci. This would help in developing elite varieties of thesespecies by employing marker assisted selections (MAS)program. Linkage maps are available for a number of fishspecies, including Atlantic cod (Hubert et al . 2010), grass carp(Xia et al. 2010), sea bream (Massault et al. 2010).Though Indian carps contribute about 90% of totalfreshwater aquaculture production of India, very little geneticstudies have been undertaken in these species. Only 69microsatellite loci are so far available from rohu in literature(Das et al. 2005, Gheyas et al. 2006) and there is no linkagemap so far generated in any of the Indian carp species. Linkagemapping involves measurement of recombination frequenciesin the parental gametes as evidenced by co-inheritance patternsin offspring. A key consideration during map construction isselecting suitable mapping populations in order to exploitmaximum polymorphism. A number of different types ofpedigrees such as F1, F2 and backcross (BC), doubled haploid(DH) recombinant inbred (RI) lines are used for the purpose,depending on the requirement. Inter-specific hybrid generatedfrom mating of closely related species is one of the strategiesto increase polymorphism between parental pairs. Therefore,the objective of the present investigation was to evaluatetwo mapping pedigrees one intra-specific (rohu × rohu) andanother interspecific rohu × kalbasu (L. calbasu) pedigreeby studying Mendelian segregation and linkage relationshipamong available rohu microsatellite loci.Rohu and kalbasu have 25 pairs of chromosomes (Zhanget al . 1991) and produce viable F