Why is Down syndrome a recessive trait?

Answer 1

Down syndrome is not a recessive trait. Down syndrome is caused by a third copy on chromosome 21 and is present at conception or shortly after. It is mostly a random (and relatively common) occurrence, unless it is of the translocation type which is rare and genetic. Therefore it is NOT a trait.

Answer 2

Down syndrome is not necessarily a recessive trait, per se, since you can have differing degrees of Downs. Additionally, recessive trait would imply inheritance from parents caused the disorder, and in most cases this is not true. Down syndrome is cause by an extra chromosome on the 21st chromosome, this is usually a result of a nondisjunction event, that is improper cellular division during embyronic development, not as a result of inheriting parental allells.

While Downs can be influenced by family history, it is not generally considered a recessive trait, as recessive would imply either the individual has it, or dosen't, with no intermediate. However there are many variable intermediates for people with Downs, from those who are barely effected and only show some physical characteristics to those who are profoundly retarded.