Triploidy caused by endoreduplication in a human zygote obtained after in-vitro fertilization.

Cytogenetic analysis of a presumably tripronuclear zygote revealed that triploidy was caused by an endoreduplicated 46,XX complement. The remaining chromosomes yielded a hyperhaploid karyotype of 28,Y, +2, +3C, +D. The origin of this chromosomal composition is obscure. Besides endoreduplication in a normal 23,X oocyte pronucleus and fertilization by a normal 23,Y spermatozoon, an additional female pronucleus might have been formed due to an irregular chromosome distribution during second meiotic division. On the other hand, penetration by a hyperhaploid spermatozoon cannot be excluded with certainty.