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CARNEGIE INSTITUTION OF WASHINGTON
GENETICS RESEARCH UNIT
COLD SPRING HARBOR, NEW YORK 11724

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Hi Al-- APR 28 1971

7
How do you define a chromosome? When I wrote that review, I had in
mind a regular mechanism of segregation (e.g. mitosis) to define the
chromosome. This does break down in the light of present knowledge
of prokaryotes. F is a shadowy intermediate. Apart from its poten-
tiality for integration (episome), you can chhose to look at it as

a chromosome or as a plasmid. We will face the same problem with
mitochoddrial DNA too. My main purpose in defining '‘plasmid' was
to stress the ambiguity of plasmagehe/virus. I think I would still
leave it at the original definition of "extrachromosomal <gene(e)>".