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Home Q & A Board Biology-Related Homework Help Genetics and Developmental Biology
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Julian Julian
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11 years ago
Is down syndrome where the entire chromosome is duplicated, meaning the proteins are duplicated as well or just every gene on the chromosome is duplicated?  So, meaning, when DNA replicates, do proteins replicate as well?  Or just the DNA strands?
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#1
11 years ago
Down's syndrome is trisomy-21, meaning that instead of having a pair of chromosome 21, a person has three. This occurs because of failure of the two homologs or sister chromatids of chromosome 21 to separate during meiosis, when gametes form. So, one of the gamete has 2 instead of one, and when it combines with a normal gamete (with one), the zygote ends up with three 21st chromosomes.

And yes, the entire chromosome is duplicated. Proteins are synthesized from the DNA sequence on the chromosomes, and because there is more DNA content coding for the same protein, I guess more amount of transcripts for mRNA will be made, and more proteins synthesized.
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#2
11 years ago
It is a extra chromosome.
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buidoi87_2009buidoi87_2009
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11 years ago
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#4
11 years ago
"Dude" gave a good answer.  

1) The 'typical' Down syndrome person has trisomy 21: an extra copy of that chromosome.

2) But Down syndrome can also be caused by a translocation, where only part of chromosome 21 gets duplicated.  So the affected person has the normal number of chromosome 21's, but one of them has an extra segment attached to it.  And that extra segment is the part that, when present in 3 copies, causes Down syndrom.

3) Proteins are not duplicated, just the genes.  Now, having an extra copy of those genes does result in more of those proteins being synthesized, but that is different than the proteins themselves being duplicated.  Proteins, unlike DNA, are temporary molecules - they are synthesized and degraded continually.
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