Sex related embryo development

Although sexual dimorphic development in the mammalian embryo prior to differentiation of the gonad has been documented, there are many seemingly conflicting observations and gaps in our understanding of this process. Conditions that influence the process include gamete interaction, that might give one sex an advantage in the fertilization process and in rates of blastomere cleavage that would allow one sex to accumulate cells at a faster rate. In this scenario, males could accumulate more cells within a defined window of development. Another key difference between males and females is the number of copies of genes located on the sex chromosomes. Transcripts from the Y-chromosome are thought to function as transcription factors, which could accelerate development. Conversely, the X-chromosome contains genes that code for rate limiting steps in pathways key to embryo metabolism and stress reduction. It can be envisioned that prior to X-chromosome inactivation in females, elevated levels of transcripts for such genes may enable greater protection from environmental stress and regulate growth. As we gain a better understanding of how males and female develop we will be able to exert greater control over the manipulation of the sex ratio for the offspring of domestic animals. (C) 2000 by Elsevier Science Inc.