M1 family size?
cutler at gpu.utcc.utoronto.ca
Thu Apr 22 15:13:54 EST 1993
Dear Arabidopsis Community,
My name is Sean Cutler, I am a graduate student of Peter McCourt's
at the University of Toronto. I'm currently screening for mutations
which affect seed development in Arabidopsis. I have a question which
I've been thinking about since I started screening for mutants, and I
thought I'd put it out to the community to see what people think. Before
I ask however, I thought I should pretext the question with a statement
that I understand that there is no 'right' answer to the question; I ask
because I'm curious as to what other people think and do.
So here it is. It's quite simple. How many M1 do you think should be
used in a screen to identify new genes?I know the safe answer.
If you look at Koorneef's data from 1982 (Mutation research) he
showed that mutation frequency per locus (using 10 mM EMS, 24 hrs.)
varies in Arabidopsis from about 1 in 20,000 for gl type mutations to
as high as 1 in 2,400 for several ga genes. The average rate was around
1 in 5000.
Based on a Poisson distribution of mutation events, you should
screen an M1 family large enough to theoretically contain at least 5
mutants in a gene to be 99% certain that you will observe that mutant
at least once. If you assume that 1 in 20,000 is a safe number for the
lowest EMS mutation rate, then the 'safe' way to screen would be to
screen M2 seed from an M1 family of at least 100,000 M1 plants. With a
genetically effective cell number of two , this drops to about 50,000.
(the GECN allegedly varies, so perhaps a GECN of 1 should be assumed
To screen M2 seed from this many M1 is a large task. How
do people generally deal with this? Should a screen which is going to
be published be done to saturating limits? I know the answers to these
questions can be very personal, but I'd like to know how people feel
I'll be happy to summarize the responses to my question.
Sean Cutler: cutler at gpu.utcc.utoronto.ca
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