Bioscientifica Proceedings

Summary. The mammalian sex chromosomes evolved from an ordinary pair of autosomes during evolution. Unlike the X chromosome that is highly conserved, the Y chromosome is poorly conserved among mammalian lineages. Several special features set the Y chromosome apart from the rest of genome: male-limited transmission, absence of recombination, abundance of Y-specific repetitive sequences, degeneration of Y-linked genes during evolution, acquisition of autosomal g...

Abstract. Although the manipulation of animal genomes has a history of more than three decades, there are only a few of the reported genetically modified (GM) animals that have passed safety regulations and found their way through to market. The production and safety regulations of GM livestock are hindered by a variety of issues, most importantly, lack of embryonic stem cells (ESC) in livestock species and concerns around the nature and biosafety of the genom...

Summary. During folliculogenesis a group of growing preantral follicles becomes responsive and dependent upon gonadotrophins, especially FSH, for their continued growth and differentiation. However, most of these follicles undergo atresia. The mechanisms that result in survival of a specific number of ovulatory (dominant) follicles appear to depend upon: (a) responsiveness of preantral follicles to gonadotrophins, (b) inhibitory and stimulatory factors from a ...

Summary. Behaviour in pigs is sexually dimorphic as early as 1 month of age; mounting of penmates is observed more frequently for males than for females. This mounting reaches its highest frequency during the 2nd month of life and then declines to a low frequency in prepubertal pigs. During the prepubertal period (3-5 months of age), bipotentiality of sexual behaviour is apparent in boars because they will not only mount oestrous females but they are also...

Summary. Seasonal variations of reproductive ability have been demonstrated in male and female sheep and goats. For the female, there is a distinct breeding season. Whilst there are large breed differences in the duration of the sexual season, oestrous cycles generally start when daylength is decreasing and end when daylength is increasing. In some breeds, ovulation without oestrus occurs during the non-breeding season. Although males are able to mate all the ...

Summary. Prolactin and LH are required for the maintenance of normal luteal structures during early pregnancy in the ewe, whilst luteolysis, induced by prostaglandin F-2α is inhibited by the presence of the conceptus. The trophoblast also secretes a local anti-luteolytic factor, trophoblastin, which is most probably a protein because it is thermolabile and inactivated by pronase. It is soluble at pH 9.6 and can be separated on Ultrogel. Trophoblastin is p...

The hypothalamo–pituitary–gonadotrophic axis develops in the sheep fetus from midgestation to late gestation. The GnRH neuronal centres seem to be fully developed in the fetus and their localization complies with the adult pattern. Pituitary gonadotrophs are responsive to exogenous GnRH and release LH and FSH in a pulsatile fashion; the highest concentrations in plasma are found during late gestation. In sheep, maturational changes of this axis continue through to ...

Abstract unavailable© 1987 Journals of Reproduction & Fertility Ltd...

Abstract unavailable© 1987 Journals of Reproduction & Fertility Ltd...

Summary. Phylogenetics is the study of evolutionary relationships among species. Phylogenies are based on the comparison of large numbers of characteristics among species. Traditionally, the field of phylogenetics was dominated by paleontologists so the characteristics studied were structural, often skeletal. The field of phylogenetics was revolutionized in the 1980s as scientists began using molecular data, first amino acid, then nucleotide sequences. This le...