Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. They are made of protein and one molecule of DNA, which contains an organism's genetic instructions, passed down from parents. In humans, animals, and plants, most chromosomes are arranged in pairs within the nucleus of a cell.
The XY sex-determination system is the sex-determination system found in humansmost other mammalssome insects Drosophilasome snakes, and some plants Ginkgo. In this system, the sex of an individual is determined by a pair of sex chromosomes. Females typically have two of the same kind of sex chromosome XXand are called the homogametic sex.
Scientists have separated the sperm which carry X and Y chromosomes, in a study which could one day have "colossal" implications for choosing the sex of animals including humans. Sperm carry either an X or Y chromosome, which helps to determine the sex of offspring in most mammals. In general, X and Y-carrying sperm are swimming about in semen in equal numbers, which explains why the human population, for instance, is made up of more or less equal numbers of males and females.
Despite most parents ultimately just wishing for a healthy baby, there are many cultural and social factors that can drive the desire for a baby of a particular sex. The medical technology for sex selection of embryos has existed in Australia for many years, but such an option is only available for medical reasons, such as sex-linked chromosomal disorder. This leaves parents who do have a gender preference looking for natural ways of predetermining the sex of their baby. In the s, the idea that timing sex around ovulation can tip the odds in favour of a girl or a boy was popularised by Shettles and Rorvik in the best-selling book How to Choose the Sex of Your Baby.
Still others lack the energy to finish the long journey through the female reproductive tract, or they get snared in sticky fluid meant to impede all but the strongest swimmers. For the subset of a subset of spermatozoa that reach their trophy, the final winner would be determined by one last sprint to the end. The exact identity of the sperm was random, and the egg waited passively until the Michael Phelps of gametes finally arrived.
Become a Friend of Aeon to save articles and enjoy other exclusive benefits. Aeon email newsletters are issued by the not-for-profit, registered charity Aeon Media Group Ltd Australian Business Number 80 This Email Newsletter Privacy Statement pertains to the personally identifying information you voluntarily submit in the form of your email address to receive our email newsletters.
Verified by Psychology Today. How We Do It. Here is why: I well remember discussing this with a Swiss veterinary professor back in the s.
Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote.
Preconceptual sex selection is still a highly debatable process whereby X- and Y-chromosome-bearing spermatozoa are isolated prior to fertilization of the oocyte. The aim of this study was to separate X- and Y-chromosome-bearing spermatozoa using methods based on the viability difference between the X- and Y-chromosome-bearing spermatozoa. A total of 18 experimental semen samples were used, written consent was obtained from all donors and results were analysed in a blinded fashion.