What determines the sex of a baby?

Donna Hill Howes, RN
Donna Hill Howes, RN
Family Practitioner

In humans, the sex of the baby is determined by the sperm. The sperm gamete is heterogamatic because approximately half of them contain the X chromosome which will result in a girl and approximately half of them contain the Y chromosome which will result in a boy. On the other hand the ova gamete is homogametic, in other words all its cells possess the X chromosome. Thus the ova gamete does not influence the baby’s sex. Therefore when a sperm penetrates the ova and fertilization occurs there are two possible outcomes: XX or a girl and XY or a boy.

Continue Learning about Fetal Development Basics & Pregnancy

How are fingerprints formed in the womb?
Many environmental factors influence the formation of fingerprints, even the exact position of the f...
More Answers
How often should I feel my baby move during pregnancy?
Fetal movement counting in pregnancy is an important way to monitor your baby's health. Learn more f...
More Answers
When does the fetus develop reflexes?
A fetus develops plenty of reflexes, and all of these reflexes depend on the central nervous system....
More Answers
When does the sense of smell develop in a fetus?
That ability starts at about 30 weeks; before that time, tissues plug up the nasal cavities.
More Answers

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.