It's really impossible to say a given organism is x percent of one parent
and x percent of another parent in any sexually reproducing species, much
less when the cross is between genera or classes or kingdoms. For example,
if you unite cells of different species and genera, often chromosomes of one
of the two various parents drops out. When human cells are united with
various plant and fungi species, the human chromosomes are quickly and
invariably (with present technology) eliminated as the line divides and
grows.
Rye has 7 pairs of chromosomes, bread wheat has 21 (3 genomes of 7). The
hybrid of rye and wheat has 28 chromosomes. In meiosis, the rye and wheat
chromosomes often pair and exchange chromatin, because of the physical
compatibility of rye and wheat chromosomes. The resulting gametes have
various numbers of chromosomes depending on where the nuclear envelope forms
after the first division of meiosis. Unreduced gametes often result. These
28 chromosome gametes would be "1/4 rye" as far as the genetic material
carried by the chromosomes (7 of the 28 chromosomes were from the rye
parent). But there is also genetic material in the cytoplasm which comes
with the female parent. So if rye is the female, the unreduced gametes on
the hybrid are more than 1/4 rye.
A selfed wheat-rye hybrid could be an almost infinite combination of
"percentages of rye and wheat," depending on how many chromosomes pass
through the meiotic division which eventually resulted in the pollen.
Some of the old plant cytogenetics texts, or any paper by Ernie Sears would
clarify this better than I could.
A good website is:
http://lausd.k12.ca.us/~kmcmahon/AP%20Bio%20Lectures/Meiosis/MLCG.html
I don't know any good places for up-to-date info on tissue hybrids between
plants and higher vertebrates, but I'll bet monsantan (sp.?) would know.
-----Original Message-----
From: Klaus Wiegand <WIEGAND@lufa-sp.vdlufa.de>
To: James Kotcon <jkotcon@wvu.edu>; sanet-mg@ces.ncsu.edu
<sanet-mg@ces.ncsu.edu>
Date: Thursday, September 09, 1999 3:09 AM
Subject: Re: Breeding and speciation (was food labeling)
hello james,
> I do not believe any consensus exists among scientists as
>to how much genetic divergence is needed to name a new species. In
>some bacteria, a single gene difference will lead to a new species
>name, while in other bacteria, as much as 30 % of the genome may
>vary within the same "species".
it might even be more. take X triticale for example, sth. like an
interbreed between rye and wheat. at first you get about 50:50 for
the relation of wheat:rye, but if you breed this line and cross it
with a pure wheat, you get something like 75:25, or if crossed with
a pure rye, a relation of 25:75.
i once asked a breeder: is that still a real triticale? and i heard
a loud YES. when i asked: if you go on with mixing the lines and
you got just only 10% of rye, that's still a triticale ? again a
definite YES. when i asked: "what about 5 %?" he said: "depends on
which 5%, you would have difficulties to see it in a single plant,
but certainly you can distiniguish them, when you compare it with a
pure wheat or pure rye."
so what he said, was that the divergence in a "true"
triticale can lie at least between 5 and 95% and it's still
considered a X triticale.
Klaus Wiegand
Landwirtschaftl. Untersuchungs- u. Forschungsanstalt (LUFA)
(Governm. Inst. for Agricult. & Environm. Res.)
67346 Speyer, Obere Langgasse 40 (GERMANY)
Dept. of Seed Sci., Microscop. Analysis & Plant Pathol.
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