Right after fertilisation, your baby becomes an embryo with its gender already set. In the early weeks, all embryos look the same, and there are no clear signs of boy or girl until around week six. After that, differences begin to show as hormones start their work.
For a male embryo, the Y chromosome triggers the development of testicles, and these release hormones that guide the growth of male genitals. Without a Y chromosome, as in female embryos, the body naturally follows the female traits and forms ovaries and female genitals.
Do Family Genes Affect Whether You Have a Boy or Girl?
People often ask why some families seem to have only boys or only girls. The simple answer is chance, with odds staying close to 50:50 in every pregnancy. Each sperm, whether it carries an X or a Y chromosome, has the same chance of reaching the egg first. Still, sperm ratios may shift slightly because of certain genes, and this can influence patterns in a family.
It's also important to remember that after you have one child, the gender of your next child is not affected by the first. Each pregnancy starts with the same possibility of having a boy or a girl. This happens because every time conception occurs, a new sperm reaches the egg. That sperm could carry an X chromosome or a Y chromosome, and the previous baby does not influence which one reaches the egg next.
Old beliefs, such as diet or timing, claim to affect a baby’s gender, but science shows they do not make a difference. The gender is set the moment the sperm meets the egg, and nothing else changes it after that.
What Are Intersex Conditions in Babies?
Most babies are born with clearly male or female traits, but in a small number of cases, things may look less defined at birth. This can mean genitals that are not fully formed or have features from both sides. Sometimes, the outside appearance does not match the internal organs. This is known as intersex or a disorder of sex development.
These conditions affect only a small group of pregnancies and are usually noticed during scans or soon after birth. Your doctor will guide you with support, explain what is happening, and discuss whether any care is needed.
A baby’s gender comes down to the chromosome carried by the sperm that reaches the egg first. While family patterns and small genetic influences may exist, each pregnancy still begins with the same basic chance of having a boy or a girl. It is a natural process guided by biology from the very first cell!
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FAQs on How a Father's Sperm Determines a Baby's Gender: The Science Behind X and Y Chromosomes
- Do X and Y sperm move at different speeds?
Modern research shows both types move at very similar speeds. The claims that Y sperm swim faster is a myth. - Does a man’s age influence gender chances?
A man’s age can affect sperm quality, but it does not change the chance of having a boy or a girl.