When reading my textbook I noticed that in all examples but one from eight the recognition site was an even number of bases.
I wondered if this was just a co-incidence, so I took the data from this site for over a thousand known recognition sites and put it into a spreadsheet (XLS uploaded here). The results are probably best summarised graphically:
Stats Test: Chi Squared Goodness of Fit.
Null Hypothesis:
There is no significant difference between the number of restriction sequences
that are an odd or even length.
|---------|----------|----------|-----|-------|----------|
| Trait | Observed | Expected | O-E |(O-E)^2|(O-E)^2 /E|
|---------|----------|----------|-----|-------|----------|
| Odd | 172 | 231.5 |-59.5|3540.25| 15.293 |
| Even | 291 | 231.5 | 59.5|3540.25| 15.293 |
|---------|----------|----------|-----|-------|----------|
Chi Squared Value = 30.586
P=0.05, 1 Degree of Freedom: Critical Value of 3.841
H0 rejected with 95% confidence (indeed with 99.9%+ confidence)
Can anyone explain or suggest why it is more common that restriction enzymes recognition sites have an even number of bases?
Updates
- Expanded dataset to include new recognition sites from the resource that 96well linked to.
- Removed all duplicate recognition sites leaving 465 distinct recognition sequences (my fault for not removing them in the first instance)
- Ran stats test on the data
- See Previous Version