Lesson: Chapter 20 — Heredity

20.6. Genetic disorders 2 of 8 Reset answers

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Question 2

A carrier woman (X^HX^h) and an unaffected man (X^HY) have children. What fraction of their sons is expected to have haemophilia?

A One half B All of them C One quarter D None

The right answer is the one marked above.

One half. The two boxes that produce sons are X^HY and X^hY. One of the two has the condition.

None of the daughters is affected, because each receives an X^H from her father. One in four of all the children — one in two of the sons — has haemophilia.

Answer the question to continue.