Genetic analyses which are relevant to plant and animal studies, rather than human populations, have specific limitations in relation to the genetics of schizophrenia. Some reviewers of family studies of schizophrenia have drawn the conclusion that schizophrenia and bipolar disorder do not share the same genetic etiologies whereas others argue that they often do. Considerable effort has been focused on genetic linkage analysis of schizophrenia employing genetic markers in multiply affected families to identify which chromosomal regions harbor susceptibility genes. This approach must take into account the complication of heterogeneity of linkage in which a number of susceptibility genes localized to different chromosomes contribute to the development of schizophrenia. The chapter describes a selection of genes that have been implicated in susceptibility to schizophrenia by cytogenetic, linkage and/or association studies. Twin and adoption studies have shown that the family environment has no influence on the etiology of schizophrenia.

Cytogenetic abnormalities of the human oocyte, as described by Pellestor, are remarkably common and there appears to be a multifactorial effect of maternal ageing. Aneuploid embryos are common following in vitro fertilization (IVF), even in unstimulated cycles. Egg freezing has proved to be technically much more difficult than embryo freezing. Ovarian failure is an untreatable condition but the opportunity for pregnancy can be restored by egg donation. Success rates are high and are maintained with increasing age. If the uterus cannot support a pregnancy, for example because of fibroids, or if the potential mother is too unfit for pregnancy, surrogacy will be required. In reviewing the uses of assisted reproduction, some 'abuses' have been revealed. The infertile couples seeking help can be desperate for treatment and therefore be vulnerable to suggestion. Reproductive tourism is burgeoning, driven by women's needs for treatment but also by commercial interests.

A number of research and clinical studies have confirmed high frequency of cytogenetic abnormalities in human oocytes and embryos. Chromosomal imbalance in oocytes can result from loss or gain of individual chromatids or whole chromosomes. The underlying causes remain to be fully elucidated, but important modifying factors include the number and location of chiasmata and maternal age. Aneuploidy is a major cause of congenital abnormalities, mental retardation, and miscarriage. However, most of the chromosome abnormalities detected in human embryos are likely to be lethal at very early embryonic stages, and are probably incompatible with the formation of a clinical pregnancy. Many fertility clinics now screen the embryos produced during in vitro fertilization (IVF) cycle in order to identify those that are chromosomally normal. Screening the oocytes/embryos from these patients for aneuploidy using PGS may be particularly beneficial in terms of IVF outcome.

Premature ovarian failure (POF), sometimes termed premature menopause, is an enigmatic disorder. Among the various causes of POF that now have been identified, it is clear that some are present only in those who have no oocytes remaining, whereas others may be associated with remaining follicles and offer the potential for ovulation and spontaneous pregnancy. The causes of POF include cytogenetic abnormalities of the X chromosome, enzymatic defects, defective gonadotropin secretion or action, environmental insults, and autoimmune disorders. The objectives of the evaluation of young women with hypergonadotropic amenorrhea are to identify any treatable causes and any potentially dangerous associated disorders. It is important to make the diagnosis in a timely fashion. In vitro fertilization with donor oocytes is the most effective way of providing a pregnancy for any affected woman, but should be used with caution in women with Turner syndrome and the fragile X premutation.