Substitution Per Mb

Question

[sunhanice]

In the sequencing papers, there always have the figure like above,

I wonder what does 'per Mb' in the y-axis mean?

for example, I can calculate no of substitutions, in intergenic, intronic,Non-coding exon, and coding exon regions.

Does it mean I need to go to calculate the following :

no of substitutions in genomic / length of genome * 1,000,000

no of substitutions in intergenic / length of intergenic region * 1,000,000

no of substitutions in intronic / length of intronic region * 1,000,000

no of substitutions in non-coding exon / length of non-coding exon region * 1,000,000

no of substitutions in coding exon / length of coding exon region * 1,000,000

In the beginning I have thought I just need to divide the no the substitutions by the length of genome then times 1,000,000. But I found the length of the genomic bar is shorter than intergenic bar, so they must be divided by the different number.

Could you please explain this for me? thanks in advance.

Answer 1

[Zev.Kronenberg]

In this graph the genome is broken into 6 classes. Each class represents a percentage of the genome. Within each of the classes the researchers simply count the number of times they see a mutation across that entire class length.

A hypothetical example.

6 mutations seen in coding exons.

coding exon length of the genome = 3 Mb

6 mutations / 3Mb = 2 mutations / Mb

this is what they are plotting: 2 (substations per megabase)

[sunhanice]

thanks for your help