Detection of genes with deleterious alleles in an inbred line of tilapia (Oreochromis aureus)

An increase in the viability of gynogenetic progeny has been recorded in Bar Ilan University (BIU) by following four successive generations of meiogynogenetic Oreochromis aureus. This augmentation is suggested to be the result of reduction in the number of deleterious alleles. The genome of progeny of the fourth successive generation of meiogynogenetic O. aureus was screened with 76 microsatellite DNA markers to identify polymorphic loci. Twenty polymorphic markers were tested for segregation distortion in four crosses of informative progeny to identify linkage to genes with recessive deleterious alleles. Significant distortion (P<0.0001) from the expected Mendelian segregation was identified for three unlinked markers: UNH159, UNH216 and UNH231. A significant deleterious effect (P<0.05) was detected in at least two crosses for each of the three markers. The onset of the deleterious process occurred between days 4 and 8 after fertilization in family 2 for UNH159 and UNH216 with significant epistatic interaction (P≤0.0001) between the two loci. In family 4, the onset was shown to occur by day 4 in early spawns and at a much later developmental stage in late spawns. The differences detected in marker effect among crosses and between spawns of the same cross indicate that complex mechanisms are involved. DNA markers linked to genes with deleterious alleles can aid in identification and elimination of those alleles from inbred lines of O. aureus.