Reader Comments

Post a new comment on this article

A query for authors

Posted by fstahl on 21 Oct 2012 at 23:23 GMT

The extreme variation in the ratio of CO and GC events observed along chromosomes together with the negative relationship between CO and GC rates therefore seem to be inconsistent with the “counting model” while supporting a more dynamic one involving a variable DSB repair pathway or DHJ resolution across genomes.

The report that the GC/(GC+CO) ratio (0.83) is so close to that which fits the Counting Model for Dm as determined by Foss et al. (1993, and others) (0.80) supports that model. However, the present authors suggest that a negative correlation between GCs and COs in various regions argues against the model. That argument looks OK for the elementary model, in which counting begins anywhere on the chromosome. However, Foss et al. (1993) also considered a model in which counting starts the centromere with a run of four GCs followed by a CO. This model was put forth to deal with the recognized shortage of COs at Dm centromeres. Such a restriction on the elementary model has the consequence of tying the distribution of COs to a chromosomal landmark, while still making interference dependent on linkage distance (centimorgans) rather than physical distances (eg., kilobases). This feature of the model tends to concentrate COs in regions of the chromosome, at the expense of GCs and could contribute to the observed negative correlation noted above. This statistically naïve Commenter would like to know whether tying the counting register to one or another, or any of several chromosome features could rescue the Counting Model.

No competing interests declared.