genome size and library screening

[Zeev Lev]

>The "ballpark" in our lab for screening genomic libraries of D.
>melanogaster is to screen 1 x 10^6 plaques (one million) in order to get a
>fair representative of the genome. What kind of numbers do you employ?
>
>Furthemore, how much larger than Drosophila melanogaster is the genome of
>Musca domestica? Then how many plaques would it be necessary to screen to
>obtain a fair representation of that genome?
>
>Susan Glueck
>sg32 at cornell.edu

The genome sizes of D. melanogaster and M. Domestica are 1.65x10^8 and
8.4x10^8 bp, respectively. To isolate a specific sequence from a library
with 17 kb inserts (probability of 99%, P = 0.99) you have to screen (only)
4.5x10^4 and 2.3x10^5 plaques, respectively (1). The appropriate numbers for
a mammalian library are 3x10^9 bp and 8.1x10^5 plaques (2). 

(1) Molecular Biology LabFax, T. A. Brown (1991), Blackwell Scientific
Publications (available from Sigma); 
(2) Molecular Cloning, Sambrook et al., vol.2, p. 9.3.

Zeev Lev