Question

A child has a 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.

1. What chromosomal event has likely occurred?
2. 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?

Answer 1

B: The mother has four derivative chromosomes, however, has all the genetic material.

In general, the derivative chromome is the result of multiple chromosomal abberrations which may involve single or multiple chromosomes. However, the centromers remains intact. The intact centromere helps in the tranfer for genetic material via replication. The good health of mother can be attributed to the presence of all the genes though on the different chromosomes than the normal case. The developemental delay of mother can be linked to genomic imprinting effect of the adjacent genes which are otherwise not the case.

A: child has excess material from chromosome 9 and 14 and too little from chromosome 10.

This may have happened during the meiotic division, where the deletion of the genetic material have caused due transfer of duplicated genetic material and deletion of few genes or chromosomal segments.

Its is shown with the example below.