Final answer:
Trisomy 13, Trisomy 18, and Trisomy 21 are the three autosomal trisomies that can result in individuals surviving past birth, with Trisomy 21 being the most common and the most compatible with longer life.
Step-by-step explanation:
The three trisomies for complete autosomes that are well-defined and compatible with postnatal survival are Trisomy 13, Trisomy 18, and Trisomy 21. These conditions occur when an individual has three copies of one of these chromosomes instead of the usual two. Trisomy 21, known as Down Syndrome, is the most common and is associated with a spectrum of characteristic physical and developmental features. Trisomy 13 and 18 also result in distinct clinical symptoms and are associated with shorter life expectancies than Trisomy 21. These trisomies can occur due to nondisjunction events during meiosis, where chromosomes fail to separate properly, leading to gametes with an abnormal number of chromosomes.