A fertility clinic records the sex chromosome carried by samples of human gametes.
| Gamete sample | Number carrying X\text{X}X | Number carrying Y\text{Y}Y |
|---|---|---|
| Egg cells | 200 | 0 |
| Sperm cells | 297 | 303 |
One sperm fertilises one egg. An embryo with XX\text{XX}XX develops as a girl and an embryo with XY\text{XY}XY develops as a boy.
Explain how these data show that the sperm determines whether an embryo develops as a girl or a boy and why approximately equal numbers of girls and boys are expected.
186 exam-style questions on OCR GCSE Biology 5.1 Inheritance, covering 5.1.1 The genome, 5.1.2 Environment and phenotype, 5.1.3 Variants and mutations, 5.1.4 How genetic variants influence phenotype, 5.1.5 Asexual and sexual reproduction, 5.1.6 Haploid and diploid, 5.1.7 Meiotic cell division, 5.1.8 Single gene inheritance, 5.1.9 Predicting single gene crosses, 5.1.10 Sex determination, 5.1.11 Multiple gene inheritance, and 5.1.12 Development of our understanding of genetics. Each one has a worked solution and a mark scheme showing where the marks go.