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  #1  
Old 04-03-2010
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Genetics Duchene Muscular Dystrophy Genetics Question?

A 23 yr old woman seeks genetic counseling because her brother has Duchene Muscular Dystrophy. Her brother has the deletion in the DMD gene. Although her mother doesn't have the gene deletion, the individual is told that her risk of the DMD gene is greater than that of the general population.
Which of the following best explains this increase risk?
a. De novo gene mutation
b. Locus heterogeneity
c. Maternal germ line mosaicism
d. Promoter mutation
e. X-inactivation
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Old 04-03-2010
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I think answer is C
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Old 04-03-2010
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Yep C maternal germ line mutation
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  #4  
Old 04-04-2010
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Wait a minute
Isn't it X-Chromosome inactivation!
X-linked recessive diseases are not seen in females because of the Lyon phenomenon
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Old 04-04-2010
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if the brother got DMD because of a de novo mutation, the sister chance will only be as the general population not more.... so its not A



in mosaicism of germcell lineage some ova of the mother r normal others r abnormal. hence the higher chance of the daughter



definition of germcell lineage mosaic mutations: mutation that occurs early in development and affects only some germ cells..other germ cells r normal and all somatic cells r normal.


moreover, X-linked recessive diseases are diseases which if mother is a carrier transfer %age to the sons is 50% and they (male babies) will show da signs because they have only 1 x chromosome... whereas if a father is a carrier he will trasfer it to all his daughters who will be carriers.

so in this case its the male baby who is manifesting the disease transferred from mother... so its C


if it would have been barr body inactivation, then sister would havebeen menifesting the disease but she is just a carrier so it cant be E
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Old 02-14-2011
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thank u doctorF.. you really cleared the concept!!
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