Re: Re; Hormesis or not ( number of chromosomes )

["Christian Hofmeyr" <chris.hofmeyr@webmail.co.za>]

Bjorn,

Thanks for your learned exposition; I require some

'translation' by an expert.  It would seem that chemical

agents like colchicine are very efficient at chromosome

doubling in certain plants, e.g. grain types, probably much

more than irradiation.

Chris Hofmeyr

Chris.Hofmeyr@webmail.co.za



> >Sorry to hark back to an old thread, but the question of

> the reaction of plants to radiation reminded me that a

> plant geneticist once told me that the irradiation of

> plant seeds can effect a doubling of the chromosomes

> (visible under a microscope), and that such plants with a

> double set usually have superior properties. Could that

> be termed a hormetic effect?

> ----

> On Mon, 26 Jan 2004 10:09:14 +0000

 "Bjorn Cedervall" <bcradsafers@HOTMAIL.COM> wrote:

> This seems to be about mechanisms in evolutionary biology

> regardless of the cause.

> 

> A doubling of the number of chromosomes (from the diploid

> state with two sets, 2n) can probably occur in a few

> different ways:

> After a normal doubling of the number of chromosomes

> there is a "cell cycle checkpoint" to make sure that

> there normally is no second doubling after the first one

> without first going through cell division. If such an

> error occurs and is transmitted to the next generation it

> must be related to the meiotic events forming the germ

> line cells.

> More common is certainly hybridization where two closely

> related species fuse to form a tetraploid (4n) or a

> tetraploid and a diploid fusing to form a hexaploid (6n)

> and so on. G L Stebbins had some publications in the late

> 1940s relating to the complex ploidy patterns in the

> grass genus Bromus (for a summary, See CP Swanson,

> Cytology and Cytogenetics, 1968, pp.511-512)

> etc.

> 

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