D. J. S. Hetzel

A genetic linkage map of the bovine genome

A cattle genetic linkage map was constructed which marks about 90% of the expected length of the cattle genome. Over 200 DNA polymorphisms were genotyped in cattle families which comprise 295 individuals in full sibling pedigrees. One hundred and seventy–one loci were found linked to one other locus. Twenty nine of the 30 chromosome pairs are represented by at least one of the 36 linkage groups. Less than a 50 cM difference was found in the male and female genetic maps. The conserved loci on this map show as many differences in gene order compared to humans as is found between humans and mice. The conservation is consistent with the patterns of karyotypic evolution found in the rodents, primates and artiodactyls. This map will be important for localizing quantitative trait loci and provides a basis for further mapping.

The conservation of dinucleotide microsatellites among mammalian genomes allows the use of heterologous PCR primer pairs in closely related species.

The high degree of polymorphism displayed by DNA microsatellites makes them useful as DNA markers in linkage studies. A search of the DNA sequence databases revealed that the locations of dinucleotide microsatellites are often conserved among mammalian species, enabling the prediction of the presence of DNA microsatellites using comparative genetic data. In closely related species such as cattle and sheep, this conservation was close enough to allow PCR primers designed for use in one species to be used to analyze microsatellite length polymorphism in the other. A total of 48 sets of primer pairs, flanking bovine microsatellites and giving polymorphic PCR products in that species, were tested with template DNA from sheep, horses, and humans. Specific products were obtained in 27 cases (56%) with ovine DNA, 20 of which (42%) showed polymorphisms. With equine DNA, 3 (6.2%) gave specific but monomorphic products, while no specific products were obtained using human DNA. The ability to use heterologous PCR primers, coupled with comparative mapping information will facilitate the use of DNA microsatellites in gene mapping studies in closely related species such as cattle and sheep, rat and mouse, or primates.

Characterization of 65 bovine microsatellites

Microsatellites or simple sequence repeat (SSR) polymorphisms are used widely in the construction of linkage maps in many species. High levels of polymorphism coupled with the ease of analysis of the polymerase chain reaction (PCR) have resulted in this type of maker being one of the most widely used for genetic analysis. In this paper we describe 58 polymorphic bovine microsatellites that were isolated from insert size selected bovine genomic libraries. Primer sequences, number of alleles, and heterozygosity levels in cattle reference families are reported. Chromosomal locations for 47 of these microsatellites as well as for 7 previously described systems derived from entries in the Genbank or EMBL databases have been determined. The markers map to 24 syntenic or chromosomal locations. Polymorphic bovine microsatellites were estimated to occur, on average, every 320 kb, and there is no evidence of clustering in the genome. Thirty of the bovine-derived microsatellite systems gave specific and polymorphic products in sheep, adding to the number of useful markers in that species.

The development and application of genetic markers for the Kuruma prawn Penaeus japonicus

Microsatellite and Amplified Fragment Length Polymorphism (AFLP) DNA markers have been characterised for use in establishing pedigrees, linkage mapping and identifying Quantitative Trait Loci (QTL) influencing commercially important traits in P. japonicus. Low efficiency of Microsatellite characterisation from P. japonicus genomic DNA, due to the high frequency and extended length of simple sequence repeats, make these DNA markers unsuitable for linkage mapping studies. Unique sequence flanking repeats necessary for PCR primer design were difficult to obtain due the extended lengths of the repeats. Microsatellites that were characterised displayed between 4-24 alleles and heterozygosities between 47-91% in unrelated animals. No P. japonicus derived microsatellite successfully amplified sequences in P. monodon, P. esculentus or P. stylirostris. AFLPs were developed as an alternative to microsatellites. Over 570 polymorphic loci were defined using different primer combinations. AFLPs are robust with some polymorphisms conserved across families. PCR amplification and sequencing of excised bands allowed development of Sequence Tagged Sites from AFLPs. A primary linkage map based on a three generation pedigree, genotyped at 246 AFLP loci has been constructed. It incorporates 129 markers in 44 linkage groups with an estimated genome coverage of approximately 57%.

Response to selection and heritability for growth in the Kuruma prawn, Penaeus japonicus

Abstract Divergent selection for High (H) and Low (L) growth was carried out for a single generation with the aim of measuring response to selection and heritability of growth in Penaeus japonicus . H and L growth (weight at 6 months of age) parents were selected from a commercial prawn pond which had been stocked with post-larvae from wild caught broodstock. Offspring of H×H, L×L and reciprocally mated (H×L, L×H) parents were reared and grown out in laboratory tanks. The direct response to one generation of selection averaged 10.7%, being 8.3% for high growth and 13.1% for low growth. Responses at other ages averaged 5.7, 6.9 and 7.9% at 3, 4 and 5 months, respectively. The average realised heritability for weight at 6 months of age was 23.4% which did not differ significantly from the estimate from the regression of offspring on mid parent of 27.7% It was concluded that the heritability of growth in P. japonicus is moderate but that rates of response to selection will be high largely due to the high levels of natural variation.

The γ fibrinogen gene (FGG) maps to chromosome 17 in both cattle and sheep

The γ fibrinogen gene (FGG) was localised in both cattle and sheep using in situ hybridisation. The probe employed was a 1-kb bovine cDNA fragment. Based on observations of QFQ-banded chromosome prepa

Genetic markers for the Booroola fecundity (Fec) gene in sheep.

Animals from the Booroola line of Australian Merino sheep are characterized by a high ovulation rate that can be attributed to the presence of a codominant allele (FecB).The specific function of the gene has not been identified. Effective use of the trait within the sheep breeding industry requires one or more genetic markers that can distinguish between alternative alleles at the locus Fec. With a combination of DNA minisatellite markers and polymorphic protein markers, a cluster of seven minisatellite fragments has been identified as being linked to the Fec gene and to the ovine A blood group locus. The minisatellite fragments have been derived from multilocus probes and hence cannot be used to define the chromosomal location of the Fec gene or to serve as diagnostic markers for Fec. The derivation of cloned single locus markers from the minisatellite fragments will enable finer scale mapping of the Fec and the A blood group locus in sheep.

The cosmid CSSM25 assigns syntenic group U2 to bovine Chromosome 9 and is localized to ovine Chromosome 8

The cosmid-derived microsatellite CSSM 25 has previously been shown to map to bovine syntenic group U2 by link-age and hybrid somatic cell analysis. We have mapped the cosmid by fluorescent in situ hybridization to bovine Chromosome (Chr) 9q17-21 and ovine Chr 8q17-21 and hence assign U2 to Chr 9 in cattle. Bovine Chr 9 and ovine Chr 8 show strong banding pattern homology, and the localization of CSSM 25 to the same region confirms the strong conservation of gene locations on these chromosomes.