is a genetic variation associated with characteristic facial appearance, learning disabilities, and physical abnormalities such as heart valve disease.

Down syndrome

Explanation:

Down syndrome is a genetic disorder that occurs when an abnormal cell division results in an extra copy of chromosome 21. Some symptoms of this syndrome are distinct facial features (small ears, small head, flat face, etc.), short height and even heat defects.

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explanation:

"a.) well–developed vascular system."