Only a few targets of the sex determining genes are known - <i>dsf, fru, </i>and the <i>yps. </i> Such genes would be expected to fit into one of three categories: (i) Genes expressed exclusively in one sex; (ii) Genes expressed at a higher level in one sex than the other; (iii) Genes that are expressed at similar levels in both sexes, but produce sex-specific transcripts. In an attempt to isolate genes that fit into these categories a non-gonadal differential screen of an adult body genomic DNA library was performed, using sex-specific radio-labelled cDNA. The genomic recombinant fs(1) was chosen for further analysis based on its preferential hybridisation to female non-gonadal cDNA. Screening of cDNA libraries using fs(1) sequence isolated two cDNAs, a 3.0kb cDNA (cDNA^A) and a 4.5kb cDNA (cDNA^B). Sequence analysis revealed that both these cDNAs encoded a novel opa repeat-containing serine/threonine protein kinase, the difference in the cDNAs being the length of the 5' and 3' untranslated regions (UTRs). The gene, which maps to polytene position 61A, was named <i>Drosophila serine/threonine protein kinase@61 (Dstpk61). </i>Northern analysis showed there to be at least 4 different <i>Dstpk61 </i>transcripts: a 3.0kb testis-specific transcript (possibly represented by cDNA^A); a 3.5kb ovary-specific transcript; a 4.5kb female-specific carcass transcript (possibly represented by cDNA^B); and a slightly larger non-sex-specific transcript. The work presented here shows that <i>Dstpk61</i> is a complex gene that produces multiple transcripts by using alternative promoters, alternative polyadenylation sites, and alternative splicing. It is now known to have significant sequence and functional homology to mammalian Phosphoinositol-dependent kinase 1 (PDK1), which has been implicated in the insulin signal transduction pathway and the regulation of apoptosis. Four mutant P-insertion lines have been identified that disrupt <i>Dstpk61</i> at different sites. The phenotypes of these mutants, possible <i>Dstpk61</i> transcripts, and the observed mRNA expression pattern are discussed in relation to the possible role of Dstpk61 protein in <i>Drosophila</i> development.

No description available.

The ubiquitin system forms the major pathway for selective degradation of abnormal, damaged and short-lived proteins in eukaryotes. Ubiquitin becomes attached to substrate proteins to target them for degradation via three types of enzyme: ubiquitin activating enzymes (E1), ubiquitin conjugating enzymes (E2), and ubiquitin protein ligases (E3). E1 enzymes are only necessary to activate ubiquitin and transfer it to an E2 enzyme. Many E2s are present within a eukaryote, and some can ubiquitinate substrates without the aid of an E3 enzyme. Studies in <I>Saccharomyces cerevisiae </I>have shown particular E2s function in processes as diverse as DNA repair, peroxisome biogenesis and cell cycle control. Much of the substrate specificity for ubiquitination is thought to reside within ubiquitin conjugating enzymes. Control of protein levels by selective degradation is important for cell differentiation and developmental processes. To allow specific spatial and temporal distribution of proteins which are key regulators of development, highly selective degradation is required. Ubiquitin-dependent proteolysis also appears essential for developmentally programmed cell death. The experiments in this thesis describe attempts to address the role of the ubiquitin system in development using <I>Drosophila melanogaster </I>as a model system. As ubiquitin conjugating enzymes are thought to each ubiquitinate a subset of proteins, these were the enzymes investigated. Four E2 enzyme genes had previously been cloned in <I>Drosophila, </I>and a further E2 was identified by a polymerase chain reaction screen. The gene was cloned, sequenced and named <I>UbcD4 </I>(ubiquitin conjugating enzyme in <I>D</I><I>rosophila </I>number 4). <I>UbcD4 </I>encodes a protein homologous to bovine E2<SUB>25K</SUB> and yeast UBC1. All five E2 genes were investigated for developmentally regulated transcription. High levels of E2 mRNA were observed in adult females, early embryos and larvae, suggesting specific developmental roles for the ubiquitin system at these stages. Ubiquitination may have a major function in the developing central nervous system, as RNA from all known E2s was found to be abundant in this tissue in embryos.

No description available.

No description available.

The <I>mariner </I> transposable element <I>mos</I>1, isolated from <I>Drosophila mauritiana</I> belongs to a family of inverted repeat DNA transposons, found in many phyla. Members of this family of elements transpose by a 'cut and paste' mechanism, in which the element is excised from its position in the genome and inserted elsewhere. <I>Mos</I>1 is 1286bp long, and contains a single open reading frame of 345 amino acids. This ORF encodes a transposase which is essential for the transposition mechanism. The existence of various forms of extrachromosomal copies of transposons has been documented for a number of elements and it has been assumed that some of these are intermediates in transposition. Active <I>mariner</I> elements exist in the genome of <I>D. simulans</I>. Several forms of free copies of <I>mariner</I> have been isolated from DNA prepared from this species. Some of these are circular in conformation. Sequence analysis, performed to determine the structures across junctions of the circular copies, has revealed that all elements are deleted for some <I>mariner</I> nucleotides. The majority of elements are missing three bases from one or the other end. Recombinant <I>mos</I>1 transposase purified from <I>E. coli</I> is able to stimulate excision of <I>mos</I>1 elements from plasmids. These excised copies are linear in structure. Primer extension analysis has been employed to investigate the terminal most nucleotides of these elements. The excision of <I>mos</I>1 occurs, leaving the terminal most three base pairs from each 5' strand behind in the plasmid. No circular copies were detected in this reaction. An explanation for these findings is discussed and a model for transposition of <I>mos</I>1 and <I>mariner </I>elements from <I>D. simulans</I> is proposed.

The aim of this thesis was to investigate the features that underpin the Group Nucleus breeding scheme for pigs in which the population is subdivided into several herds. With Best Linear Unbiased Prediction it is possible to directly assess response. The estimation is, however, dependent on the underlying variance components used. In general, estimating breeding values with an inflated heritability in the model results in a high predicted response, whilst having much less of an effect on the actual response. Additionally, the reduction in the weight of family information results in more unrelated animals being selected. A method to utilise this effect in order to reduce inbreeding is presented. As the population is subdivided across farms, analyses were undertaken to determine genetic and phenotypic parameters both within and across farms; little heterogeneity of variance occurred for litter size. The low heritability of the trait does however confirm the need for specialised selection methods in order to achieve satisfactory response. The production traits also showed low heritabilities, but with up to twofold differences between farms. Further analyses of the data indicated that this heterogeneity of variance was due in part both the environmental differences and a sire by farm environment interaction. The effect of altering the proportion of artificial insemination (AI) to link farms was investigated. In general, the rate of response is robust to changes in proportion of AI matings for all but the lowest proportion AI, mainly because both AI boars and natural service boars (only used in a single herd) are highly selected. Moveover, the increased number of boars associated with natural service, for example at 90% compared to 100% AI, can yield greater responses in the long term due to a lower rate of inbreeding and consequently a larger available additive genetic variance. In summary, the theoretical studies indicate that a Group Nucleus population is a robust system in which to implement genetic selection with alternative testing procedures, proportion AI or parameter use effective for all but the most extreme cases. In practice, however, additional factors can cause low heritability estimates and subsequently low rates of predicted responses, and these are discussed.

The interpretation of genetic diversity within subdivided populations is a difficult problem. This thesis develops new theory for its interpretation, and applies it to the problem of within river variation in Atlantic salmon (<I>Salmo salar</I> L.) populations which have been the subject of many surveys of genetic diversity throughout their range. These surveys have found lower levels of genetic variation than many fish species, even those occupying similar environments such as the Brown Trout (<I>Salmo Trutta</I> L.). Genetic differentiation has been observed both between samples from different rivers, and from samples from different tributaries of the same river. The levels of differentiation are of considerable interest from both scientific and commercial reasons. Despite the intense study the reasons behind the levels of differentiation between populations are unclear, and it is uncertain whether there are distinct stocks of fish within rivers. As an attempt to understand this differentiation and to guide any future studies new mathematical and statistical models for the riverine environment are developed. The riverine environment within which salmon breed is unlike any of the previously produced models for genetic differentiation. This thesis shows that the branching pattern within rivers can lead to a distinct pattern of variation which is unlike that seen in linear habitats. These habitats may lead to increased differentiation between populations. A stochastic approach to genetic variation, the coalescent process, allows us to separate the processes involved in the production of genetic data, into the genealogical and mutational processes. This approach allows us more flexibility in the modelling of genetic data. The various processes which have been invoked as causes for the observed genetic variation are analysed using these new tools.

No description available.

No description available.