Down syndrome is

The correct option is Chromosomal.

Down syndrome is classified as a chromosomal disorder because it is caused by an abnormality in the number of chromosomes, rather than a mutation in a single gene (which would classify it as dominant, recessive, or sex-linked).

Typically, human cells contain 23 pairs of chromosomes, for a total of 46 chromosomes. However, Down syndrome occurs due to a cell division error called non-disjunction during the formation of reproductive cells, which results in an extra copy of chromosome 21. This condition is also known as Trisomy 21.

Because individuals with Down syndrome have three copies of chromosome 21 instead of the usual pair, they have a total of 47 chromosomes in their cells. Since this genetic alteration involves the duplication of an entire chromosome, it is categorized as a chromosomal condition.