Scientists decode chromosome related to Down syndrome

2000/05/10 Roa Zubia, Guillermo - Elhuyar Zientzia

• Genetika
• Osasuna

It is one of the smallest chromosomes in the human genome but of great importance

This CHROMOSOME is characterized by its relationship with Down syndrome. In our genome we have twenty-three pairs of chromosomes. One of the 700 children born has another copy of chromosome 21, that is, instead of being a couple has a threesome. When this happens, Down syndrome develops. It is not a mere mental slowness, a disease that can cause abnormal growth, heart disease, leukemia and early Alzheimer's.

It is unclear why having a third copy of this chromosome is a problem. At least it is known that all the genes on this chromosome have nothing to do with it. Knowing the sequence can help a lot to clarify everything. In fact, those affected by Down syndrome are less likely to have solid tumors, as chromosome 21 encodes the gene for a tumor destruction protein. Increased protection against many types of cancer. But not against leukemia.

In addition to Down syndrome, chromosome 21 has other specific characteristics. A type of Alzheimer's disease, amyotrophic sclerosis, and a type of epilepsy are caused by the mutation of local genes. Fourteen have already been identified.

This chromosome stores the total code of genes 225. This size is small. Chromosome 22, decoded last year, contains the code of genes 545. However, the first and last have 33.8 and 33.4 million base pairs, respectively. This also means that what has been sequenced now is somewhat smaller. It is very curious. Much of chromosome 21 is useless, at least in the coding field.