Lesch‑Nyhan syndrome is an X‑linked, recessive condition caused by mutation of the HPRT1 gene responsible for purine metabolism. The syndrome is characterized by juvenile‑onset gout, involuntary muscle movements, and behavioral disorders. A mother and father have a young daughter who was

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Explanation:

The concluding part of the question can be seen in the attached image.

The correct answer would be that the father did not contribute a sex chromosome to his daughter due to nondisjunction of the sex chromosome. The daughter is XO and her only X chromosome came from the mother who is a carrier.

Since the mother's maternal grandfather had the syndrome and there is no history of it in the father's family, the daughter must have inherited an affected chromosome from her carrier mother. Normal females have two X chromosomes - one from each parent - and would therefore require two affected chromosomes in order for X-linked diseases to manifest in them.

In this case, the syndrome manifested in the daughter because she lacks one X chromosome - a situation caused by a missing X chromosome in the father. Hence, the daughter is XO instead of XX and the single chromosome is an affected chromosome from the carrier mother.

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