I am doing a presentation for my class on down syndrome and i need to know why it isn't dominant or recessive. p.s. i need a simplified answer

Seek info here: Lots of HT doctors have answered this for others - here's a start. Just dig a bit further, but it's a good reply. Source: HealthTap, https://edc1.healthtap.com/user_questions/22610

Not a trait: Down syndrome happens when an extra 21 chromosome is present in all the cells of the body. It happens before conception when the donor egg fails to shed one of its 21 chromosomes in the formation of the egg ; the male 21 joins the female pair ; creates an embryo with 3 number 21's. It has nothing to do with traits or mutations in the gene code.