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Title: Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy Post by: maryp630 on Oct 28, 2013 Trisomy 21
Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy usually results from nondisjunction during meiosis. In some cases, however, the extra copy results from a translocation of most of chromosome 21 onto chromosome 14. A person who has had such a translocation in his or her gamete-producing cells is a carrier of familial Down syndrome. The carrier is normal because he or she still has two copies of all the essential genes on chromosome 21, despite the translocation. However, the same may not be true for the carrier’s offspring. The diagram shows the six possible gametes that a carrier of familial Down syndrome could produce. http://session.masteringbiology.com/problemAsset/1094978/21/1094978_015.jpg (http://session.masteringbiology.com/problemAsset/1094978/21/1094978_015.jpg) Suppose that a carrier of familial Down syndrome mated with a person with a normal karyotype. Which gamete from the carrier parent could fuse with a gamete from the normal parent to produce a trisomy-21 zygote? Drag one of the white cells (representing gametes) to the white target in the diagram. Drag one of the pink cells (representing zygotes) to the pink target. Title: Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy Post by: Doctor-2-B on Oct 28, 2013 Content hidden
Title: Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy Post by: chuffman91 on Nov 25, 2013 thanks!
Title: Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy Post by: thats p on Dec 1, 2013 very helpful! thanks! ^-^
Title: Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy Post by: Doctor-2-B on Feb 7, 2014 Very welcome. :)
Title: Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy Post by: spn1004 on Feb 21, 2014 Thank you so much!
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