Solution

In humans, the probability of each child being a son is $\dfrac{1}{2}$, because the father's sperm carries X or Y in equal numbers.
Each birth is independent, so the probability of four sons in four births is $\left(\dfrac{1}{2}\right)^4$.
$= \dfrac{1}{16}$

Concept Independent probability of each birth

Principles of Inheritance and Variation in past papers

198 questions from this chapter have appeared across 27 exam years.