Term: trisomy, (tri-)+ (-somic)
Origin: Anc Greek
τρία-/τρεις (= the number three)
σώμα/soma (=body) > σύμα/syma(=corpse)
In plants, first case of trisomy was investigated in Datura stromonium (Jimson weed) by Blakeslee and Belting in 1924. D. stramonium normally has 12 pairs of chromosomes in the somatic cells, but in a individual they discovered 25 chromosomes (2n + 1).
Trisomy is a deviation of normal chromosome (aneuploidy) leading to gain of one extra individual chromosomes from diploid set. In humans only three autosomal trisomies occur in liveborn infants (trisomy 13, 21 and 18).