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Question 82

Human sex is settled by which sex chromosome the fertilising sperm carries. A couple already have three sons. What is the predicted chance that their next child is a daughter?

  1. More than 50 per cent, because three sons make a daughter overdue
  2. 50 per cent, the same as for each of the earlier childrenCorrect answer
  3. Less than 50 per cent, because this couple evidently have sons
  4. It cannot be predicted at all once a pattern has appeared

Explanation

Each fertilisation is settled by whichever sperm arrives first, and the sperm involved in the next one are unaffected by the children already born. A run of sons is simply one of the sequences that chance allows, in the same way that the same result can come up several times in a row in any repeated fair process.

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Question 82: Human sex is settled by which sex chromosome the… · Genetics Basics · Questena