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More gene guns

Keith Robison robison1 at husc10.harvard.edu
Tue May 26 09:04:08 EST 1992

samodena at csemail.cropsci.ncsu.edu (S. A. Modena) writes:

>One of the primary obstacles to bioengineering miracle plants is that
>aside from a few "major" genes, most of any plants traits are controlled
>by multiple genes.  My impression is that current progress with QTL
>research via RFLP's is that multi-gene factors are not well behaved.  This
>may be surprising only to non=plant breeders.  The possible combinatorials
>involved with even 10 genes and a few alleles is astronomical.

>The idea behind bioengineering to the identify factors that are important
>and alleles that are superior.  Yet somehow, this seems to still overlook
>the combinatorals behind making those identifications.  In other words,
>why should analysis by RFLP gels be more efficient that traditional
>methods employed by breeders/geneticists?  Both suffer the same problem:
>inability to grow and screen a sufficient number of plants to identify
>the _most_ superior genetypes via phenotypes.

>Anyone have thoughts on this topic?

>|     In person:  Steve Modena     AB4EL                           |


	I'm surprised you would ask this question, since NCSU is
such a hotbed for QTL research.
	The big advantage of the RFLP technology is that you can track
ALL parts of the genome -- even those which don't have easily scorable
phenotypes. Also, scoring RFLP's is faster (and I believe cheaper) than
scoring phenotypes.
	For example, suppose you have a high-yield (HY) inbred strain of
corn and one resistant to corn borers (CBR).  Both traits are controlled
by QTL's scattered throughout the genome.  So you cross the two to
create an F1, and back-cross the F1 to the high-yield parent.  Using
old technology, you must score every F2 for borer resistance to
pick the ones to re-backcross.  And you will have to do this with each
round of back-crossing.  If instead, you have already mapped the QTL's,
then you just RFLP-score each progeny and retain only those bearing
CBR-type genome in the regions around the borer-resistance loci.  Now
backcross those to the HY strain.  In other words, at each backcross
you select progeny with the most HY genome, with the constraint that they
contain the CBR loci.  In the end, you get your result quicker while
scoring fewer progeny.

Keith Robison
Harvard University
Program in Biochemistry, Molecular, Cellular, and Developmental Biology

robison at ribo.harvard.edu 

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