When is sex determined in a fetus

Medical researchers at Melbourne's Murdoch Children's Research Institute have made a new discovery about how a baby's sex is determined -- it's not just about the X-Y chromosomes, but involves a 'regulator' that increases or decreases the activity of genes which decide if we become male or female. An embryo with two X chromosomes will become a girl, while an embryo with an X-Y combination results in a boy," Ms Croft said. High levels of the SOX9 gene are needed for normal testis development. Lead author of the study, Professor Andrew Sinclair, said that 90 percent of human DNA is made up of so called 'junk DNA or dark matter' which contains no genes but does carry important regulators that increase or decrease gene activity. If these enhancers that control testis genes are disrupted it may lead to a baby being born with a disorder of sex development.
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12.10.2019
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Am I Having a Boy or Girl? — Ultrasound & Sex Prediction

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When Can You Find Out the Sex of Your Baby? | Parents

Sexual differentiation , in human embryology , the 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 chromosomes , of which 22 are autosomes and 1 is a female sex chromosome the X chromosome. Each sperm also contains 23 chromosomes: 22 autosomes and either one female sex chromosome or one male sex chromosome the Y chromosome. An egg that has been fertilized has a full complement of 46 chromosomes, of which two are sex chromosomes.
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When Does a Baby Develop Gender?

The million dollar question for many after finding out about a pregnancy: Am I having a boy or a girl? Some people love the suspense of not knowing the sex of their baby until the delivery. Of course, only a doctor can reliably determine the sex of a baby. So if you want to know the sex ahead of time, your doctor can use different tests at different stages of your pregnancy.
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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. In the prenatal period, sex determination and differentiation occur in a series of sequential processes governed by genetic and environmental factors.
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