Date of Award

Winter 2004

Project Type

Dissertation

Program or Major

Genetics

Degree Name

Doctor of Philosophy

First Advisor

Thomas D Kocher

Abstract

Tilapia (Oreochromis species) are one of the most dominant species in the aquaculture market. Genomic approaches may contribute to tilapia culture in the near future by identifying genes controlling traits valuable at the market. One of the most important traits for farming of tilapia is sex because monosex culture shows the best efficiency of culture. In tilapia, however, the mechanisms of sex-determination have been poorly understood because of the variation in the genetic basis of sex-determination and the lack of morphological differences between sex chromosomes.

To facilitate QTL analysis of these traits, a genetic linkage map was constructed from hybrids between Oreochromis aureus and O. niloticus using CRIMAP. The linkage map consists of 25 linkage groups with about 500 genetic markers spanning 2345 cM. Using the information of the linkage map, two different chromosomal regions (LG1 and LG3) responsible for sex determination were identified in these species (O. niloticus and O. aureus). BAC clones containing genetic markers in the sex-determining regions were isolated. Shotgun and end-sequences from these BACs identified syntenic regions among Fugu, tilapia, and human. A few genes such as a DEAD box protein, Sox family, and a LIM/homeobox, seem to be good candidates for sex-determining genes, and will need further study. AFLP (amplified fragment length polymorphism)/BSA (Bulked segregant analysis) technique was performed to add more markers in the sex-determining region in O. niloticus. This method appeared to be not so efficient in this study, because, although 3 of 128 selective primer pairs were informative, none of them were closer to sex than the markers that were already identified in the sex-determining region. So, more markers should be developed to further fine map the sex-determining genes within the region.

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