Final answer:
Down syndrome is a chromosomal abnormality caused by having three copies of chromosome 21, leading to physical and intellectual impairments; it is not related to height or preventable by lifestyle.
Step-by-step explanation:
Down syndrome is a chromosomal abnormality that occurs when an individual has three copies of chromosome 21, also known as trisomy 21. This condition is caused predominantly by chromosomal nondisjunction during meiosis and is the only autosomal trisomy where affected individuals may survive to adulthood. Consequences include certain physical characteristics, intellectual disabilities, and potential health issues, but it is unrelated to a person's height or preventable by lifestyle choices like exercise and a healthy diet.
Contrary to the other statements offered, Down syndrome is not directly passed to siblings, though genetic counseling can provide likelihood of recurrence in families. The age of the mother plays a significant role in the risk of a child being born with Down syndrome, with risk increasing in women over the age of 36.