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Aneuploidy and Down Syndrome

Organisms vary widely in the number of chromosomes per cell. The ant, Myrmecia pilosula, has only two chromosomes (one pair) per cell. By contrast, the fern, Ophioglossum, has up to 1260 chromosomes (630 pairs) per cell. This variation among organisms seems to be unrelated to how complex those species are. The precise chromosome number, though, seems to be an important characteristic. So an ant with one pair of chromosomes must have just one pair of chromosomes. And a fern with 1260 chromosomes must have 1260 chromosomes. Any different number results in changes in characteristics that are often so dramatic that the organisms cannot survive.


Humans typically have 46 chromosomes (23 pairs) per cell. Human aneuploidies are conditions where the chromosome number is not 46.

Select a human aneuploidy.
Describe the symptoms of this human aneuploidy.
Explain the cellular processes that lead to this condition.
Is it possible to treat aneuploidies in utero?
In your opinion, should we treat aneuploidies in utero?

Solution Preview

You are correct in saying that chromosome number has nothing to do with organism complexity. I would certainly say that a fern is less complicated than an ant, but yet has significantly more chromosomes. Humans usually have 46 chromosomes (23 pairs). However, when certain things happen during development, this number can change.

Probably the most common aneupoidy is referred to as Down Syndrome. This occurs when a person ends up with an extra 21st chromosome. Instead of having 46 they have 47. Down Syndrome (which I suggest you investigate further to find out more about it) results in several general physical features that indicate a person has the syndrome. These include:

Spot on the colored parts of the eyes
Decreased muscle tone
Short, stubby fingers
Short neck, with excess skin at the back of the neck
Flattened facial profile and nose
Upward slanting ...

Solution Summary

This response offers an example of a human disease that results from aneuploidy. It discusses the symptoms of Down Syndrome and evaluates whether people with these types of genetic disorders can be treated in utero.