Sexual differentiationin human embryologythe process by which the male and female sexual organs develop from neutral embryonic structures. The normal human fetus of either sex has the potential to develop either male or female organs, depending on genetic and hormonal influences. In humans, each egg contains 23 chromosomesof which 22 are autosomes and 1 is a female sex chromosome the X chromosome.
Embryos with XY chromosomes become boys, and those with XX chromosomes become girls. That means that all our sex organs come from the same foundations: The testes in men are equivalent to labia and ovaries in women, and the penis is the equivalent of the clitoris. At around week 7the Y chromosome signals for the start of testosterone production, and male genitalia begin to develop.
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.
NCBI Bookshelf. Sex differences of importance to health and human disease occur throughout the life span, although the specific expression of these differences varies at different stages of life. Some differences originate in events occurring in the intrauterine environment, where developmental processes differentially organize tissues for later activation in the male or female.
The tests have been available to consumers in drugstore chains and online for a few years, but their use has been limited, partly because their accuracy was unclear. One company, which guaranteed European doctors now routinely use the tests to help expectant parents whose offspring are at risk for rare gender-linked disorders determine whether they need invasive and costly genetic testing.
More about how the environment can affect sex ratios of children. The chances for a boy or a girl are a lot like the chances of getting heads. A female bluestreak cleaner wrasse can turn into a male when necessary.
Parents dying to know their baby's sex before birth can typically find out with an ultrasound at 20 weeks. But if baby doesn't provide a full frontal view — or if parents can't stand to wait 20 weeks — any number of old wives' tales promise to give answers. The latest of these, "skull theory," looks to the shape of the fetal skull.
Jamie Mastrangelo has been writing since She received a Bachelor of Arts degree in communications at Pace University where she served as managing editor of her college newspaper. She writes health and feature articles.
A Newcastle University study involving thousands of families is helping prospective parents work out whether they are likely to have sons or daughters. The work by Corry Gellatly, a research scientist at the university, has shown that men inherit a tendency to have more sons or more daughters from their parents. This means that a man with many brothers is more likely to have sons, while a man with many sisters is more likely to have daughters.
Although sonographic fetal sex determination is feasible in most pregnancies, in some cases, it may pose difficulties. An attempt to determine the fetal sex should not be made before weeks' gestation because this early, it is relatively inaccurate. Sonographic fetal sex determination in the late second trimester is based on direct visualization of the external genitalia, whereas in the late first and early second trimester, it is based mainly on the direction of the genital tubercle the "sagittal sign" : downward direction of the genital tubercle indicates a female fetus and upward direction a male fetus.