Certain aneuploidies such as trisomy-21 (Downs syndrome), trisomy-18 (Edward syndrome), Turner syndrome (XO) etc are more common than others.
I had a vague thought that it is related to chromosome size: the chromosomes which are towards the extremes of size will be affected in an improper segregation event.
Chromosomes 13, 18, 21 and Y are among the smaller chromosomes in humans, and are commonly associated with aneuploidy (but 22 which is also small is not affected). The larger ones are unaffected (X is an anomaly).
I thought that longer ones should be more affected because more cohesin bridges have to be broken, but it seems that is not the case.
- Is there any association of chromosome size and frequency of aneuploidy?
EDIT
- If the difference is because of differential lethalities then does the length correlation still hold true? Smaller the chromosomes, lesser the genes and hence lesser would be the effect of extra copy on the cellular biochemical networks.
Answer
I thought it was just that the other aneuploidies were fatal. They occur as often but miscarry earlier in the term therefore you don't see them. So basically there are only three that are viable 21,18 and the sex chromosome with a number of combinations: XO, XXY, XYY and XXX.
More information here: http://www.nature.com/scitable/topicpage/chromosomal-abnormalities-aneuploidies-290
With regard to the frequency for each chromosome:
For males (i.e., sperm; source):
The mean disomy frequency is 0.15% for each of the autosomes and 0.26% for the sex chromosomes. Most chromosomes analyzed have an equal distribution of disomy with the exception of chromosomes 14, 21, 22 and the sex chromosomes, which display significantly higher disomy frequencies.
Size of the chromosome is frequently reported as a factor in the frequency.
For females (i.e., eggs; source):
The data is obviously harder to attain. One study from IVF treatments show differences in the frequency of different chromosomes at different stages in meiosis.
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