Sexual reproduction is an evolutionary innovation that arose 1.2 billion years ago, and in that time, has allowed a rapid diversification of species outpacing that of asexually reproducing organisms. Successful sexual reproduction in animals requires the incredible coordination of complex genetic and behavioral factors; from the most fundamental levels of ensuring correct chromosome segregation and ploidy to the most complex of behavioral mating rituals, any failure can result in a complete loss of evolutionary fitness. In this thesis, I have explored the developmental programs that function to ensure somatic sex determination, sexual differentiation, and mating behaviors in C. elegans. C. elegans is an androdiecious nematode species that has been extensively characterized in regard to the sexual dimorphism of its development, nervous system, and behavioral outputs. Sex determination pathways are widely diverged across phyla, and C. elegans has coopted a Gli family transcription factor to serve as a cell autonomous global regulator of somatic sex determination. I investigated the expression of this transcription factor, tra-1, with cellular, subcellular, sex-specific, and temporal resolution in both sexes of C. elegans and found that it is dynamically regulated to control sex determination. In contrast to the upstream sex determination pathway, genes that control downstream sexual differentiation in animals display much higher functional conservation, and many of the regulators of sexual differentiation belong to a family of transcription factors known as the DMRT family. Downstream of the tra-1 global regulator, I found that the highly conserved DMRT family gene dmd-4 acts much more specifically in adult hermaphrodites to generate sexual dimorphism at the level of the phasmid sensory neurons PHA and PHB. Furthermore, the sexual dimorphism of DMD-4 is regulated post-translationally by a ubiquitin-binding domain that I also found to be functionally conserved in the human ortholog, Dmrt3. Although these transcription factors both demonstrate the high degree of genetic control that contributes to sex determination and sexual differentiation, I also described male-specific effects of early life stress on sexual dimorphic synaptic connectivity and behavior generated by the phasmid sensory neurons, indicating that sexual differentiation is also plastic to environmental cues encountered during the life of an organism. This thesis provides insight into how genetic pathways function at multiple levels to give rise to extensive sexual dimorphism in the soma of an animal, both globally and in regard to the development on individual cells, in addition to the ways in which these genetic pathways can be modified by environmental factors and organismal life history.

Thesis(M. A. Agricultural Management (Animal Production)) -- University of Limpopo, 2019 / The study was conducted to assess phenotypic and genotypic diversity in resistance to gastro-intestinal nematode (GIN) within communal goats in different agro-ecological zones of Limpopo province. Eighty goats were randomly sampled from Mopani = 20, Blouburg = 20, Vhembe = 20 and Capricorn = 20, representing four agro-ecological zones of Limpopo province. Frequencies and percentages of occurrence of qualitative traits and least square means (LSM) of quantitative traits were computed. Goats were characterized as multi-coloured (67.7%), black dominant coat colour (40%), flat face profile (73.8%), erect ears (68.75%), slopping rump (47.5%), no toggles (83.8%), horned (86.3%), while 71.0% and 59.4% were straight shaped and orientated backward respectively, in all agro-ecological zones. Faecal and blood samples were collected to assess the prevalence of GIN and genetic diversity of goats. The highest prevalence and abundance GIN parasites were Haemonchus contortus (nematode = 357.42) followed by Fasciola hapatica (trematode = 163) and Moniezia (cestodes = 121.50). The patterns of GIN prevalence varied (P < 0.05) across agro-ecological zones and seasons. Prevalence of Moniezia nematode varied (P < 0.05) amongst goat sexes, whilst prevalence of other GIN’s did not vary (P>0.05). For genetic variation in GIN resistance, goats were genotyped at 15 microsatellite markers recommended by the International Society of Animal Genetics. Expected heterozygosity (HE) ranged from 0.69 in arid zone goat population to 0.76 in sub-humid zone goat population, while the observed heterozygosity (HO) ranged from 0.53 in arid zone goat population to 0.60 in sub-humid zone goat population. Mean number of alleles (MNA) per population ranged from 6.13 to 7.40. Gene differentiation (FST) among populations was low (3.6%). The results revealed that genetic relationships between populations do not reflect their geographical proximity as revealed by the Nei’s genetic distance results. Low heterozygosity resulted in reducing some fitness traits for GIN parasite resistance. Inbreed goats showed low internal parasite resistance across all agro-ecological zones.

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Könsbestämning hos vertebrater är ett komplext område som har intresserat forskare under en lång tid, trots detta är det i dagens forskningsläge inte helt självklart vad det är som avgör kön. Syftet med denna litteraturstudie är att identifiera och sammanställa kunskap om avgörande könsbestämningsmekanismer utifrån det aktuella forskningsläget. I samband med detta kommer arbetet undersöka hur exempel från könsbestämningssystem hos vertebrater kan användas och tillämpas i biologiundervisning på gymnasiet. Arbetet kom fram till att det är flera gener och proteiner som deltar i könsbestämningen, samt att många av dessa konserverats genom evolutionen. Dock betyder inte detta att alla grupper har samma könsbestämningsmekanismer utan det fanns en stor variation mellan vertebratgrupper. Jämförelser av könsbestämningssystemen visade på nya evolutionära samband mellan genetisk och miljöbetingad könsbestämning. Avslutningsvis konstateras möjliga tillämpningar i biologiundervisningen på gymnasiet. Exempel från olika könsbestämningssystem hos vertebrater kan eventuellt användas för att ge elever nya naturvetenskapliga perspektiv på könsbestämning och utveckla biologilärarens arbete med sexualitet, samtycke och relationer. / Sex-determination in vertebrates is a complex area of research that has interested researchers for a long time, still to this day it is not entirely clear what determines sex. The purpose of this literature review is to identify and summarize knowledge about crucial sex-determining mechanisms based on the current state of research. Regarding this review it will investigate how examples from the sex determination system in vertebrates can be used and applied in biology education at high school. The work concludes that there are several genes and proteins that are a part of the sex-determination, and that many of these have been conserved during evolution. However, this does not mean that all the vertebrates have the same sex-determining systems; rather there is a large variance within the vertebrates. Comparison of the sex-determining systems revealed new evolutionary relationships between the genetical- and the environmental sex-determining system. Finally, possible applications in biology education in high school were discussed. Examples from different sex-determining systems in vertebrates could potentially be used to provide students a new scientific perspective of sex-determination and develop the teacher’s work with sexuality, consent and relationships.