Genetic Markers & Linkage Mapping Of The Ornamental Guppy Fish, Poecilia Reticulata
Researcher : Dr Gideon Khoo
Designation : Associate Professor
Faculty : Faculty of Science
Department : Department of Biological Science
Email Address : email@example.com
Background Information & Scope of Research
Genetic linkage maps are a fundamental tool with important applications for the elucidation of genomic organization and evolution, localization of monogenic and polygenic (quantitative) traits, dissection of developmental processes by mutations and studies of genetic diversity. Different classes of genetic markers, e.g., phenotypic traits, enzymatic loci, restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNA (RAPD), amplified fragment length polymorphisms (AFLPs), microsatellites and sequence tags (STSs and ESTs) have been widely used to unravel the complex genomes of several teleost species such as zebrafish, medaka, rainbow trout, tilapia and swordtail-platyfish hybrids.
Singapore and Malaysia are internationally known as ornamental fish breeding and export centres with exports of ornamental fish totalling at least US$100 million. One of the top 10 most popular ornamental fish in Singapore and Malaysia is the guppy, Poecilia reticulata, of which at least 40 different colour varieties are cultured in monoculture farms. These varieties have been developed from feral (Wildtype) guppies through intensive and continual selective breeding. The guppy has 23 pairs of chromosomes, one pair of which is the sex chromosomes (X and Y). A number of studies since the 1920's have shown that colour pattern genes are sex- (X and Y) linked and dominantly expressed whereas those controlling background body pigmentation are autosomal and recessive. Wildtype alleles of these genes express only olive-brown colouration.
Methodology & Outcome of Research
Recent studies by our research group on the interactions of colour pattern genes of domesticated guppies, namely black caudal-peduncle (Bcp), blue tail (Blt), green tail (Grt), red tail (Rdt), variegated tail (Var) and snakeskin body-snakeskin tail complex (Ssb-Sst), and the sex-determining region (SdR) with those of wild guppies such as Maculatus (Ma), Coccineus (Co), Tigrinus (Ti), Luteus (Lu), Vitellinus (Vi) and Elongatus (El), gave a putative map order of Var-(Ssb-Sst)-SdR-Ma-Co-Ti-Lu-Blt-Rdt-Bcp-Vi-El-Grt for the guppy Y-chromosome. The X-chromosome is postulated to have a similar order. Besides these phenotypic studies, there is a paucity of molecular-based mapping information for the guppy.
Molecular-based linkage maps of the guppy were constructed using Tuxedo- and Wildtype-specific, and individual-derived RAPD markers. Segregation patterns of RAPD and phenotypic markers (Bcp, Rdt and the SdR) were investigated in F2 off-spring of Tuxedo ♂ ´ Wildtype ♀ and Wildtype ♂ ´ Tuxedo ♀ crosses. Among the 300 and 276 RAPD markers scored from patterns generated by 22 primers for the respective crosses, linkages were identified for 230 and 212, respectively. The Tuxedo ♂ ´ Wildtype ♀ and Wildtype ♂ ´ Tuxedo ♀ maps spanned 2100 Kosambi centi-Morgans (cMK) and 1900 cMK, respectively, in 28 linkage groups. Average marker resolution was 10 cMK. Genome length was estimated at 4410 cMK and 4060 cMK for the respective crosses with an average physical distance of 166 kbp/cMK. Several RAPD markers were found to be closely linked or allelic to loci for the sex-linked Bcp and Rdt genes, and the SdR.
Recommendations for Future Research
These primary linkage maps are the initial step towards the construction of a high-density map to facilitate map-based cloning and marker-assisted selection (MAS) of quantitative trait loci (QTL) that are essential for the development of comprehensive breeding programs for the guppy.