An equal sex ratio followed by differential sex mortality causes overestimation of females in gall midges: no evidence for sex ratio regulation

Monogeny, the production of unisexual broods by individual females, has been recognized for nearly 80?years. The genetic nature of gall midges' sex determination predicts an equal numbers of male-producing and female-producing females in the populations such that the overall sex ratio is expected to be nearly 1:1. However, observations of some strictly monogenous populations with biased sex ratio, mainly toward females, have raised the question of whether gall midges are able to adjust their offspring sex ratio in response to changes in environmental conditions, and some authors have even considered sex ratio regulation as a strong force in the course of the evolution of monogeny. In this paper, first, by studying the sex ratio variations of the predatory gall midge, Aphidoletes aphidimyza within a generation, we showed that adult males emerge up to 1?day earlier and have shorter life span than females (less than 4?days and up to 6?days, respectively). Although, the sex ratio of A. aphidimyza at the time of emergence was nearly 1:1 (52.41?% males), a simple population simulation indicated that the differential mortality of sexes can lead to a female-biased sex ratio estimation (57.88?% females) under random sampling in the natural environments. Our results imply that the primary sex ratio of monogenous gall midges is nearly 1:1 and that the arrhenogenic/thelygenic gall midges are not able to alter the number of their male/female progenies in response to changes in environmental conditions.     

Five cases of prenatally diagnosed sex chromosome mosaicism

Prenatal detection of chromosome mosaicism is a relatively rare phenomenon and always constitutes a diagnostic problem. The difficulties are much more when the mosaics involve the sex chromosomes, because of the large phenotypic variability in individuals with these abnormalities. We studied 5 cases of true mosaics, 4 of these were prenatally detected, while 1 case was revealed only in the fetal lymphocytes after induced abortion. The limits of amniotic fluid culture with regard to the diagnosis of true mosaics and the difficulties arising in genetic counselling are discussed.     

Discordant fetal sex on NIPT and ultrasound

Prenatal diagnosis of sex discordance is a relatively new phenomenon. Prior to cell-free DNA testing, the diagnosis of a disorder of sexual differentiation was serendipitous, either through identification of ambiguous genitalia at the midtrimester morphology ultrasound or discovery of genotype-phenotype discordance in cases where preimplantation genetic diagnosis or invasive prenatal testing had occurred. The widespread integration of cfDNA testing into modern antenatal screening has made sex chromosome assessment possible from 10 weeks of gestation, and discordant fetal sex is now more commonly diagnosed prenatally, with a prevalence of approximately 1 in 1500-2000 pregnancies. Early detection of phenotype-genotype sex discordance is important as it may indicate an underlying genetic, chromosomal or biochemical condition and it also allows for time-critical postnatal treatment. The aim of this article is to review cfDNA and ultrasound diagnosis of fetal sex, identify possible causes of phenotype-genotype discordance and provide a systematic approach for clinicians when counseling and managing couples in this circumstance.     

Cell-free DNA screening and sex chromosome aneuploidies

Cell-free DNA (cfDNA) testing is increasingly being used to screen pregnant women for fetal aneuploidies. This technology may also identify fetal sex and can be used to screen for sex chromosome aneuploidies (SCAs). Physicians offering this screening will need to be prepared to offer comprehensive prenatal counseling about these disorders to an increasing number of patients. The purpose of this article is to consider the source of information to use for counseling, factors in parental decision-making, and the performance characteristics of cfDNA testing in screening for SCAs. Discordance between ultrasound examination and cfDNA results regarding fetal sex is also discussed. © 2015 John Wiley & Sons, Ltd.     

Attitudes towards sex selection in the Western world

It appears that in most Western countries, son preference is somewhat stronger than daughter preference. However, when one considers the preference of women it looks as though the opposite pattern is emerging. There is a considerable social acceptance of ‘light’ methods of sex selection (such as diets), even though these methods are not proven to be effective. The inclination to use sperm separation methods appears to be greater in the United States than in some European countries. There are indications that a preference for boys or for girls is associated with attitudes towards technology, child-rearing style and the stereotyping of boys or girls. Copyright © 2006 John Wiley & Sons, Ltd.     

Noninvasive detection of fetal sex: the laboratory diagnostician's view

Toward the end of the twentieth century it was discovered that cell-free fetal DNA sequences could be detected in maternal blood plasma. Initially, Y-chromosome sequences originating from male fetuses were targeted in cell-free DNA extracted from maternal plasma in order to demonstrate proof of this concept towards the development of noninvasive prenatal diagnosis methods. Clinical application of this approach is now possible. Fetal sex can be detected through a procedure that is noninvasive with respect to the fetus. Specifically, the presence of Y-chromosome sequences in maternal blood plasma indicates that the fetus is male, whereas lack of a signal will indicate that the fetus is female. Fetal sex can be detected very early, from at least the 7th week of pregnancy (and even earlier, according to several studies), about two months before this information is available through ultrasound scanning. Although the controversial issue of fetal sexing is not new, it is expected that with the availability of an accurate noninvasive test, public interest will rise. It is therefore imperative that an authorized committee of experts in each country generates an official policy regarding application of the test. Copyright © 2006 John Wiley & Sons, Ltd.