Gametes are cells that have the unique ability to give rise to new individuals as well as transmit (epi)genetic information across generations. Generation of functionally competent gametes, oocytes... Show moreGametes are cells that have the unique ability to give rise to new individuals as well as transmit (epi)genetic information across generations. Generation of functionally competent gametes, oocytes and sperm cells, depends to some extent on several fundamental processes that occur during fetal development. Direct studies on human fetal germ cells remain hindered by ethical considerations and inaccessibility to human fetal material. Therefore, the majority of our current knowledge of germ cell development still comes from an invaluable body of research performed using different mammalian species. During the last decade, our understanding of human fetal germ cells has increased due to the successful use of human pluripotent stem cells to model aspects of human early gametogenesis and advancements on single-cell omics. Together, this has contributed to determine the cell types and associated molecular signatures in the developing human gonads. In this review, we will put in perspective the knowledge obtained from several mammalian models (mouse, monkey, pig). Moreover, we will discuss the main events during human fetal (female) early gametogenesis and how the dysregulation of this highly complex and lengthy process can link to infertility later in life. Show less
This thesis will first document on variation in progeny sex ratios among individual female plants of Urtica dioica at our field site in Meijendel (Chapter 2). Next, we show that there is also... Show moreThis thesis will first document on variation in progeny sex ratios among individual female plants of Urtica dioica at our field site in Meijendel (Chapter 2). Next, we show that there is also considerable sex ratio variation among male and female flowering shoots in 26 natural populations studied (Chapter 3). Additionally, we studied life history traits of male and female clones to detect sex-specific differences that might have contributed to the sex ratio bias observed in the field. Our results indicate that the sex ratio bias in natural populations may be a consequence of a bias that already originated in the primary sex ratio. Next, we investigated physiological, environmental (Chapter 4) and genetic (Chapter 5) aspects of sex determination. For the latter aspect, a series of crosses including male, female and monoecious plants of U. dioica was performed. These experiments were designed to investigate whether sex ratio variation in the primary sex ratio is due to environmental sex determination (ESD) or genetic sex determination (GSD) solely or due to an interaction of both. Genetic mapping of sex-linked markers was used as a supplementary tool to analyze the genetic mechanism of sex determination (Chapter 6). Finally, to study the inheritance pattern of the sex ratio trait, crosses were performed between individual male and female plants from different sex ratio families (Chapter 7). Show less
