Chromosomal Aberrations: Which is more harmful? Deletion or Duplication?

Question

We have been studying structural chromosomal aberrations and we were asked to find out if deletion is more harmful or duplication is more harmful. Which one will cause more changes or harm?

Answer 1

Duplication, in reference to chromosomal aberrations, does not refer to trisomy where a whole extra chromosome is present.  It refers to a segment of the chromosome being duplicated.

Deletions are usually more harmful because they involve a loss of information whereas a duplication involves adding a repeated unit. Duplication events are a major source for evolutionary change because the duplicated chromosomal region can mutate without fear of losing function of the original gene.

However, there could be lots of exceptions.  For example:

1. In diploid organisms, you likely still have a normal copy of the chromosome even if one copy holds a deletion.

2. The deletion may not contain any coding DNA.

3. The duplication might insert itself in the middle of a coding region and disrupt its function.

Answer 2

Both can be pretty disastrous.   Down's Syndrome is the result of having an extra chromosome 21.  This is thought to cause an excess amount of certain amino acids in the brain resulting thereby in mental retardation, deformities, a predisposition to certain cancers (such as leukemia) and a compromised immune system.  In a similar way Turner's syndrome and Klinefelter's syndrome, both disorders of the s*x chromosomes.  

Cri du Chat syndrome, which is the result of a deletion of certain chromosomes causes severe mental retardation and a curious catlike cry in the children who have it.  

Most chromosome aberrations lead to spontaneous abortion, since the fetus dies as a result.  This is nature's way of hiting "reset" on the whole reproductive process.   Whether this is worse than having a defective child is debatable.  Probably a live-born child with serious problems is worse.

Answer 3

Well...if you are talking about a WHOLE chromosome I think deletion will merely not give offspring (in sexual reproduction) in more cases than duplication, as you see in trisomy 21 (Down syndrome), so in a way duplication is more harmful as it's more likely to not get detected on time for a natural abortion of the foetus (this happens normally in the woman if a genetic abnormality is detected by the body). Duplication is most common as it only leads to problems once a cell divides. Chromosome deletion will in most cases result in the cell dying at the next cell division, or even before as it misses a great deal of genetic information.