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General Introduction MARKER-ASSISTED SELECTION IN ENHANCING GENETICALLY MALE NILE TILAPIA (Oreochromis niloticus L.) PRODUCTION MOHD GOLAM QUADER KHAN MARKER-ASSISTED SELECTION IN ENHANCING GENETICALLY MALE NILE TILAPIA (Oreochromis niloticus L.) PRODUCTION A thesis submitted for the Degree of Doctor of Philosophy Mohd Golam Quader Khan M. Sc. (Fisheries Biology and Genetics) Institute of Aquaculture, University of Stirling Stirling, Scotland, UK February 2011 DECLARATION I declare that this PhD thesis has been composed by myself based on my own research. It has not been submitted for any other degrees. The nature and extent of any work carried out by, or in conjunction with others has been acknowledged by reference. Signature of Candidate …………………………………….. Signature of Supervisor…………………………………….. Signature of Co-supervisor…………………………………. Date ……………………………………… M G Q Khan Institute of Aquaculture i This work is dedicated to the departed soul of my mother M G Q Khan Institute of Aquaculture ii ABSTRACT All-male fry are preferred to prevent uncontrolled reproduction before harvest in intensive Nile tilapia (Oreochromis niloticus) aquaculture. Males also grow faster than females. An alternative approach to direct hormonal masculinisation of tilapia fry is to produce fry that are genetically male. However, sex determination system in tilapia is fairly complex. Recent developments have resulted in a linkage map and genetic markers that can be used to analyse the sex determination system. To analyse the genetic sex determination mechanism and to develop marker-assisted selection in the Stirling Nile tilapia population, a fully inbred line of clonal females (XX) was verified using test crosses and DNA markers (mostly microsatellites) to use as a standard reference line in sex determination studies. A series of crosses were performed involving this line of females and a range of males. Three groups of crosses were selected (each group consisted of three families) from progeny sex ratio distributions, and designated as type ‘A’ (normal XY males x clonal XX females), type ‘B’ (putative YY males x clonal XX females) and type ‘C’ (unknown groups of males x clonal XX females), for sex linkage study. For type ‘A’, inheritance of DNA markers and phenotypic sex was investigated using screened markers from tilapia linkage group 1 (LG1) to confirm the LG1-associated pattern of inheritance of phenotypic sex and the structure of LG1. Screened markers from LG1, LG3 and LG23 were used to investigate the association of markers with sex in families of type ‘B’ and ‘C’. In addition, a genome-wide scan of markers from the other 21 LGs was performed to investigate any association between markers and sex, in only families of cross type ‘B’. LG1 associated pattern of inheritance of phenotypic sex was confirmed by genotype and QTL analyses in families of cross type ‘A’. Analyses of genotypes in families of type ‘B’ and ‘C’ showed strong association with LG1 markers but no association with LG3 and LG23 markers. Genome wide scan of markers from all other LGs did not show any significant association between any markers and the sex. The allelic inheritance of two tightly linked LG1 markers (UNH995 and UNH104) in families of type ‘B’ and ‘C’ identified polymorphism in the sex determining locus: one of the alleles was associated mostly with male offspring whereas another allele was associated with both progeny (mostly males in type ‘B’ families, and approximately equal numbers in type ‘C’ families). This knowledge was used to identify and separate supermales (‘YY’ males) that should sire higher proportions of male progeny, reared to become sexually mature for use as broodstock. Two of them were crossed with XX females (one clonal and one outbred) to observe the phenotypic expression of the strongest male-associated allele in progeny sex. The observations of 98% male (99 males out of 101 progeny) and 100% male (N=75) from these two crosses respectively, suggest that a marker-assisted selection (MAS) programme for genetically male Nile tilapia production could be practical. This study also suggests that the departures from the sex ratios predicted using a “simple” XX/XY model (i.e., YY x XX should give all-male progeny) were strongly associated with the XX/XY system, due to multiple alleles, rather than being associated with loci in other LGs (e.g., LG3, LG23). This study also tentatively names the allele(s) giving intermediate sex ratios as “ambivalent” and emphasizes that the presence and actions of such allele(s) at the same sex-determining locus could explain departures from predicted sex ratios observed in some earlier studies in Nile tilapia. M G Q Khan Institute of Aquaculture iii ACKNOWLEDGEMENTS This is my pleasure to express my sincere gratitude to my supervisors Dr. David Penman and Professor Brendan McAndrew for their kind co-operation, encouragement and guidance throughout my PhD study. I also thank them heartily for patiently reading the thesis and giving valuable suggestions. I would like to thank Mrs Ann Gilmour for helping me learn the molecular biology techniques. Special thanks to Dr. John Taggart for his friendly help throughout the research work. My kind thanks are due to Dr. Rodney Wooten and Dr. Michael Leaver for their advices during every PGRC meeting. I would like to thank Professor Brian Austin, Director, Institute of Aquaculture, for his encouragement during the PhD research conference. My sincere thanks are also due to Mr. Keith Ranson and Mr. William Hamilton for providing all facilities to breed, rear and maintain experimental animals in the Tropical Aquarium System for over three years. I would like to thank Dr. Sadiqul Islam, Dr. Almas Ara, Dr. Cuit Mota, Dr. Oscar Monroig, Mr. Albert Willis, Mrs Salema Begum, Amy Halimah Rajaee, Rania Ismail, Ekrem Ayna, Sandy Miller, Ania Pino, Louise Colliar, Elizabeth Mcstay and Christos Palaiokostas for their kind help and support throughout the study. Many thanks to Charlie Harrower and Jane Lewis for their all co- operation to get my research materials out of aquastores. I offer my thanks and regards to all of my friends who supported me in any respect during my research. I can not list all the names here, but you are always in my mind. I would like to give my sincere thanks to Commonwealth Scholarship Commission for funding my PhD research. I am so grateful to my parents who brought me up with their love and blessings, and encouraged me to pursue advanced degrees. I have lost my greatest inspiration, my beloved mother some months ago. I pray to God almighty for her departed soul and thank her at this moment. I also thank my father-in-law, my brother-in-law, my sister Mary and my brother Mamun for their support and love. I would like to give my heartfelt appreciation to Jesmin Ara Milton, my beloved wife for her endless support throughout the study. I humbly thank God, the most gracious, for His mercy. M G Q Khan M G Q Khan Institute of Aquaculture iv Table of Contents Page Declaration i Abstract iii Acknowledgements iv Table of contents v List of Tables viii List of Figures x List of Appendices xi Chapter 1. General Introduction 1.1 Historical background, farming potential and production trends of tilapia 1 1.2 Significance of monosex production in Nile tilapia 7 1.3 Possible ways of all male production in Nile (and other) tilapia 7 1.4 Sex determination system in different animals 14 1.4.1 Sex determination in humans and other mammals 16 1.4.2 Sex determination in birds 21 1.4.3 Sex determination in insects 22 1.4.4 Sex determination in fish with particular emphasis on tilapia 25 1.5. Molecular markers in fish sex determination mechanisms 31 1.6 Genetic mapping in tilapia 34 1.7 Marker-assisted selection 38 1.8 Aims and objectives of the present research 40 1.9 Structure of the present thesis 41 Chapter 2. General Materials and Methods 2.1 Experimental fish and basic maintenance 42 2.2 Fish handling and breeding 43 2.3 Feeding regimes 47 2.4 Steroid food preparation 48 2.5 DNA extraction and quantification 49 2.5.1 Collection of tissue 49 2.5.2 DNA extraction 49 2.5.2.1 Phenol-chloroform extraction method 50 2.5.2.2 REAL DNA extraction protocol 51 2.5.2.3 HotSHOT genomic DNA preparation 52 2.5.3 Genomic DNA quantification 52 2.6 Polymerase chain reaction 53 2.7 Genotyping 57 2.8 Statistical analyses 57 M G Q Khan Institute of Aquaculture v Chapter 3. Validation of a clonal line of females as a reference line for sex determination studies 3.1. Introduction 58 3.1.1 Verification of gynogenetic or androgenetic inheritance 67 3.1.2 Objectives of the study 69 3.2 Materials and methods 70 3.2.1 Fish Stock 70 3.2.2 DNA extraction and quantification 71 3.2.3 Selection of DNA markers 71 3.2.4 DNA amplification 73 3.2.5 Genotyping and fragment analyses 75 3.2.6 Evaluation of sex ratios between clonal females and sex-reversed neomales 76 3.2.7 Evaluation of sex ratios involving clonal and outbred females with a range of males 76 3.2.8 Statistical analysis 76 3.3 Results 77 3.3.1 Proof of clonal nature 77 3.3.2 Sex ratios and viability in clonal lines 79 3.3.3 Sex ratios involving clonal and outbred females with a range of males 81 3.4 Discussion 82 Chapter 4. Sex linkage study in the Stirling Nile tilapia (Oreochromis niloticus ) population 4.1 Introduction 90 4.2 Materials and Methods 96 4.2.1 Screening of broodfish and PIT tagging 96 4.2.2 Breeding of fish 96 4.2.3 Selection of different types of families for sex linkage study 96 4.2.4 Fin biopsy and DNA extraction 97 4.2.5 PCR and genotyping 97 4.2.6 Genome wide
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