Question

Down Syndrome can be caused by trisomy 21 or by a Robertsonian translocation. Explain specifically how each of these mutations can happen in the cell, and why both cause the symptoms of Down Syndrome.

Answer 1

In human we have 23 pairs of chromosome. We got half of it from our father and half from mother. But in case of down syndrome, the person having it will have an extra copy or total 3 copies of chromosome 21 in place of two. This exrta copy of chromosome 21 can be a whole chromosome or part of it. Trisomy 21 generates in cell during cell division and it is happened due to non-disjunction. At the time of cell division, when sister chromatids or homologous chromosome can not separate completely, it results in aneuploidy condition or where there is abnormal number of chromosome occurs. On the other hand in Robertsonian translocation, one chromosome is broken at centromere, and the broken arm is get attached and ale a long chromosome with one cntreomere. As a result the long chromosome will contain the majority of the gene while the small part will have less amount of genetic information. This tranlocation can take plece in between homologous or non-homologous chromosome. During Robertsonian translocation, the long arm of chromosmome 21 get attached with chromosome no 14 or 15 and results in trisomy of chromosome no 21.

In both the mutation trisomy of chromosoe 21 occurs which is the common cause beind the down.syndrome.