General ScienceMadrid 2026Question 3A
A geostationary satellite
The four forces, the gravity that makes it orbit and the angular velocity: why it is solved this way
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Problem statement
Imagine a recessive disease linked to the X chromosome, in which women can be carriers. Suppose that a man who does not have the disease has children with a carrier woman.
a) Draw a diagram of the cross (0.5 marks).
b) State the percentage of normal daughters and of carriers, and that of normal sons and of those who have the disease (1 mark).
c) Give an example of a disease of this type (0.2 marks).
d) Explain the difference between phenotype and genotype. Give an example shown in the Punnett square of part a (0.8 marks).
Source: Madrid university entrance exam (PAU, Spain) · 2025-2026 · Ordinary session · General Science · Question 2A. Official exam set by the public universities of the Community of Madrid, to whom it belongs; translated from Spanish and reproduced with its source in order to explain it for teaching purposes.What this lesson answers
- What does «recessive, X-linked» mean?
- Which alleles does each parent carry, and why can a man not be a carrier?
- a) What can each parent pass on to their children?
- a) The Punnett square, box by box
- b) Which percentages come out, and out of what total?
- Another route: following each chromosome, without the square
- c) A real example: haemophilia
- d) What is the difference between genotype and phenotype?
- The four answers and how to check the square
- Common mistakes you must not make
- Exam tips
- If you want full marks
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