A phenotypically normal woman has had two children with trisomy 13. Which of the following scenarios would be least likely to result in this recurrence?
she is a germ-line mosaic for trisomy 13
she carries a Robertsonian translocation of chromosome 13 to chromosome 14
she carries a Robertsonian translocation of chromosome 21 to chromosome 14
she has had both children in her late 40s
she carries a Robertsonian translocation of chromosome 13 to chromosome 15
