A child has severe intellectual disability, developmental delay, autism and unusual facial features, His mother had a learning disability and slightly delayed development. Genome sequencing as well as karyotyping reveal that the child has excess material from chromosome 9 and 14 and too little from chromosome 10. Th mother has all of the genetic material, but she has four "derivative" chromosomes - they have seemingly mixed and matched their parts. These chromosomes consist of pieces of 9, 10, and 14; 9, 10, and 16; and 9 and 4. 

a. What chromosomal event has likely occurred?

b. How can the nature of the chromosomal event explain the mother's learning disability and developmental delay, but good health otherwise and a full genome?