TBR biology down syndrome

batista_123

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i have a question about #100 in the genetics section of TBR. They show a gel electrophoresis or whatever that thing is called and they ask did the mother or father have non-disjunction?
then the answer says from the figure, its clear that it was the mother. I have no idea why. The figure is weird because the bands are not all in the same columns they are in 3 or 4 columns. how do you tell if it was the mother or father?

by the way, if you dont understand dna sequencing, check this out:
http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter15/animation_quiz_1.html
 

dragon529

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Both mother and father have 2 columns for the 2 chromosome 21 that they have. Now, the reason that the child has down syndrome is because the child has 3 columns (3 chromosome 21). Take a look at the child's box, the left band comes from mother, the middle band comes from father, and the right bands come from mother. The mother contributed both sets of chromosomes and resulted in a kid with down syndrome.
 

batista_123

Junior Member
10+ Year Member
7+ Year Member
Aug 6, 2006
426
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151
  1. Pre-Medical
Both mother and father have 2 columns for the 2 chromosome 21 that they have. Now, the reason that the child has down syndrome is because the child has 3 columns (3 chromosome 21). Take a look at the child's box, the left band comes from mother, the middle band comes from father, and the right bands come from mother. The mother contributed both sets of chromosomes and resulted in a kid with down syndrome.

i dont understand why the mother and father have 3 bands. If a person has 2 chromosomes, shouldnt they have 2 bands?
 
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