R help - Jan 2011 - A question regarding volcano plot

Hello all,

I was trying to make a volcano plot with some real data, using log2(ratio)
vs. Z-value significance.
However the scatter of the points is too less contrary to 'normal'
volcano
plots  and I'm getting a  sharp 'V' shaped plot.

*Am I doing something wrong here?*

The data(ratio) is available from pastebin:

http://pastebin.com/m2Jss3qF

data <- read.table("data.txt",header=FALSE)
ratio <- data$V1
ratio.mean <- mean(ratio)
ratio.sd <- sd(ratio)
ratio.log <- log2(ratio)

z <- (ratio-ratio.mean)/(ratio.sd)

z.sig <- 2*pnorm(-abs(z))
z.tsig <- 2*pt(-abs(z),df=length(ratio)-1)#sig from t-dist

par(mfrow=c(1,4))

plot(ratio.log,-log10(z.sig))
plot(ratio.log, -log10(z.tsig))
plot(ratio.log,z.sig)
plot(ratio,z)

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I forgot to mention the plot looks like this :-(

http://img402.imageshack.us/i/volcanoi.jpg/

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