Question

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?

Answer 1

As stated, the mother has all the genetic material but still there is mix matching of some parts of the four derivatives like 9&10, 14&9, 10 &16, 9&4.

A. There is condition in which some of the chromosomes gets mix matched or rearranged named as Chromosomal translocation.

It has two types balanced translocation and unbalanced translocation.

In balanced translocation, when the chromosomes get mismatched with no increase or decrease in the genetic material. There is full functionality of genes.

In unbalanced translocation, when the mismatching of chromosomes results in increase or decrease of genetic material.

In the mother, the full genetic material is available which means she has balanced chromosomal translocation.

B. As she has balanced chromosomal translocation, the genes are fully functional. But the slight developmental delay and learning disability which is caused by mismatching of some chromosomes together.

But her health has no deformity because there are particular combination of chromosomes which produce diseases like translocation of (11&14) causes Mantle cell lymphoma, t(9 & 22) cause chromicchromosomeous leukemia etc.

Luckily, her mother translocations does not result in formation of particular combination which will result in particular health condition and all of her genes are also fully functional.