Look at DFA results

Examine chromosome analysis results

This program presents the results of a Detrended Fluctuation Analysis on Chromosome 22, and allows the user to manipulate those results to predict where exons might be located.

Please choose your analysis parameters:

Choose a data set:
(Note: data sets are identifed by chromosome number, whether the DFA walk was done with "C+T" or "A+T" conversion, and the chunk size.):

Choose a starting chunk:

Choose an ending chunk:

Modify the expression below, or enter a different expression to predict that a chunk is part of an exon. The following variables can be included in the expression (typed exactly as they appear):

sequence_slope
sequence_correlation
walk_slope
walk_correlation
GC_percentage (which is really a "proportion" greater than zero and less than or equal to 1.0)

Use "or" or "||" for logical OR and "&&" or "and" for logical AND:

( ( ( sequence_slope > .45 ) and ( sequence_slope < .75 ) ) and ( ( walk_slope > 1.44 ) and ( walk_slope < 1.65 ) ) ) and ( GC_percentage > .52 )

Show exon list

Show data values for chunks intersecting exons

Show data values for exons intersecting chunks

Choose a data value to graph along with the known and predicted gene/exon locations:

Sequence slope
Sequence coefficient
Proportion of G+C bases
Walk slope
Walk coefficient

Choose a graph size: Small Medium Large Huge

Interpretation of DFA results:

According to Peng, et al. in "Quantification of scaling exponents and crossover phenomena in nonstationary heartbeat time series" (CHAOS, Vol. 5, No. 1, 1995), a straight line (a line with a high regression coefficient) produced by a DFA run "indicates the presence of scaling," and the slope of the line indicates the nature of that scaling:

a sequence with a slope between 0. and .5 indicates a sequence "such that large and small values of the time series are likely to alternate."

a completely random series produces a straight line with a slope of .5,

a sequence where relatively large observations tend to be followed after some interval by additional larger observations, should produce a slope between .5 and 1.0.

slopes of, or close to, 1.0 indicate a 1/f power-law relationship, a series possessing dependencies at many, or all, time scales examined, (sometimes indicative of a system at a "critical point)."

slopes above 1.0 are no longer of a power law form; a slope of 1.5 is produced by Brownian motion.

Additional information

For more information about this program examine " Using Detrended Fluctuation Analysis to identify exons" and/or contact Michael Grobe.