Sex Determination
In humans, sex is determined by the sex chromosomes, with females XX and males XY.
▶ Interact
Play with the controls to see the idea in action.
📘 Learn
In humans, sex is determined by the sex chromosomes, with females XX and males XY.
- The father's sperm decides the baby's sex
- Each pregnancy has a 50 percent chance of either
- The Y chromosome carries the male-determining gene
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Sex Determination?
Within Biology, which covers cells, the human body, genetics, evolution, plants and ecosystems: the science of living things, this topic explains Sex Determination. Biology topics show how living things work, from the cell up to whole ecosystems, with models you can explore step by step.
Check that you can explain Sex Determination in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Sex Determination helps you explain how living things stay alive and respond to their surroundings, which is central to biology exams.
Sex Determination in detail
Human body cells have 23 pairs of chromosomes, and one pair determines sex. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The Y chromosome carries a gene that triggers testes development.
All eggs carry an X chromosome, and sperm carry either X or Y, so the sperm determines the sex of the baby. There is a 50% chance of a boy or a girl at each pregnancy, shown with a Punnett square. Some traits, like red-green colour blindness, are carried on the X chromosome, so they are more common in males.
How the interactive helps you understand Sex Determination
Click a card to flip it and reveal the answer, then move on to the next one.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Sex Determination.
Real-life uses and examples
- Explain how Sex Determination helps a living thing stay alive, using a plant or animal example.
- Connect Sex Determination to health, food and medicine in everyday life.
- Use Sex Determination to interpret a diagram, graph or microscope image from a practical.
Common mistakes to avoid
- Using everyday words, such as “energy” or “bad”, without their scientific meaning.
- Listing the steps of a process without saying how one step causes the next.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Sex Determination
What is Sex Determination?
In humans, sex is determined by the sex chromosomes, with females XX and males XY.
What are the most important points about Sex Determination?
The main points are: The father's sperm decides the baby's sex; Each pregnancy has a 50 percent chance of either; The Y chromosome carries the male-determining gene.
Why is Sex Determination useful?
Understanding Sex Determination helps you explain how living things stay alive and respond to their surroundings, which is central to biology exams.
How can I practise Sex Determination?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Sex Determination?
Related topics in Biology include Natural Selection, Extinction, Cloning.