Burdick, A. B.
Linkage group V is composed, roughly, of cf 16 lf-j 32 a 23 f while linkage group X is made up of vt 35 nt. Butler put these two groups together on the basis of recombimtion data between wt and lf-j and Rick and Barton took them apart again on the basis of trisomic tests of a and wt and also because their recombination data did not show linkage between vt and lf-j. vt gave trisomic segregation with chromosome 7 while a gave no trisomic ratios with any chromosome tested, which included all but 3 and 6. I would like to take part, in this fray on the side of Butler who ignobly has abandoned his original position in view of the trisomic data. I can't refute directly the trisomic data but I will show why I think vt and lf-j belong to the same linkage group and chromosome.
I must start by accepting the adversary's conclusion the wt is on chromosome 7. To this must be added the accumulated wt - lf-j linkage data of table 1 which includes my results of last summer. With the exception of
Table 1
VARIOUS REPORTED VALUES FOR RECOMBINATION BETWEEN lf-j AND wt
Author BC F2
___________________________________________
Fcgle & C. .30 +- .04 .32 +- .02
Butler .375 +- .01
Butler .405 +- .01
Rick & B. none none
Burdick .453 +- .02
Burdick .405 +- .02
Rick and Barton's data, the linkage values are all significant and are
associated with significant Chi-square components for linkage. This indicates
(contrary evidence notwithstanding, that groups V and X are on the same
chromosome 7. I still can't account for a not showing trisomic ratios with
chromosome 7 but I choose to ignore this for the time being rather than to
ignore the accumulated wt - lf-j linkage data.Now I have a linkage group very roughlyy, as follows: wt 40 cf 16 lf-j 32 a 23 f I put 40 units between wt and cf because I think the loose linkage between wt and lf-j indicates that these genes (wt and lf-j) are more than 50 units apart.
Next, because it pertains to the nature of this linkage group, I would like to stir-up another old question the question of whether lf and j are one or two genes. MacArthur got about .2% recombination between these two genes but neither Rick nor I have ever been able to find a recombinant. But still, they might be two genes because:
1. They have different and unrelated effects.
2. The gene sp will modify lf but not j.
3. They lie in the chromatic region around the centromere of chromosome 7 and therefore don't recombine.
This last point I draw from the evidence that lf-j is in the middle of my linkage group and from Barton's evidence that the center half of chromosome 7 (and several others, also) is chromatic and that chiasmata do not occur in chromatic regions (at least not in the all-chromatic short arm of 2). This gives us the very interesting possbility of having two genes located in the supposedly inert chromatic material and offers a chance for study of the nature of these differentiated areas. The linkage situation and the fact that lf and j do not recombine serve to suggest this location but, regardless of whether I'm right about the linkage group, the conjecture that they lie in a chromatic region can be valid.