Genes that cause Prader-Willi syndrome and Angelman syndrome are closely linked
ID: 8898 • Letter: G
Question
Genes that cause Prader-Willi syndrome and Angelman syndrome are closely linked along chromosome 15. Although people with these syndromes usually do not reproduce, suppose that a couple produces two children with Angelman syndrome. The oldest child, Pat, grows up and has two children with Prader-Willi syndrome. The second, Robin, grows up and has one child with Angelman syndrome.a. Are Pat and Robin's parents both normal or does one of them have Angelman or Prader-Willi syndrome? If one of them has a disorder, explain why it is the mother or the father.
b. What are the sexes of Pat and Robin? Explain how you determined this.
Explanation / Answer
This is a great question. It requires you to understand the basics of mendelian genetics but you also need to know about PWS and AS. Thats because these diseases dont follow normal inheritance patterns, but rather patterns called "imprinting". No I'm not a geneticist, but I am in medical school so we do actually learn about these sorts of things. What's "imprinting"? Imprinting means that certain genes are only expressed if they are passed down from a parent with a specific sex. In this instance, PWS is expressed only if the gene comes from a male, and AS is expressed only if the gene comes from the mother. Thinking about it another way, if PWS comes from your father it will be expressed as the dominant trait, but if it comes from your mother it will be expressed as AS instead, which has different symptoms than PWS. For more discussion, read this wikipedia article: http://en.wikipedia.org/wiki/Genomic_imprinting#Prader-Willi.2FAngelman Now back to the question: Pat has two children with PWS, meaning he must be male (since only males have offspring that express this trait) and Robin must be female since she has a child with AS (again, only women pass on this trait to offspring that express the defect). If Pat has AS, he must have inherited the disease from his mother. So to summarize: A) Pat and Robin's mother have the disease (impossible to know if it is expressed as PWS or AS based on the question) B) Pat is a man and Robin is a woman. Hope that helps! Jonathan
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