Selective Recombination System in Bombyx mori. I. Chromosome Specificity of the Modification Effect.

The effect of modifiers on recombination frequency between Ze and lem loci on chromosome 3 to elucidate the chromosome specificity of modification and the distribution of modifiers using Bombyx mori lines selected for high (H) and low (L) recombination rates between the p(S) and Y loci in chromosome 2 was investigated. By crossing to the Z (Ze lem/++) line, the recombination rate between the p(S) and Y loci in chromosome 2 was decreased from 28.18 to 23.33 in the H line and was increased from 4.92 to 16.05 in the L line. On the other hand, the recombination rate between the Ze and lem loci in chromosome 3 was increased from 16.21 to 20.21 in the Z line by crossing to the H line, but also increased to 19.02 by crossing to the L line. The significant correlation observed between the transformed recombination rates of chromosomes 2 and 3 in the (Z x L) x L backcross indicated that there were common factors modifying recombination frequency in chromosomes 2 and 3 or different factors linked to the same chromosomes. In the family of L x [(Z x L) x L] backcross, the distribution of transformed recombination rates indicated that there were several factors in the remaining chromosomes which were modifying recombination frequency in chromosome 2 but not in chromosome 3. It was also indicated that these factors were linked to different chromosomes than are the factors modifying recombination frequency in chromosome 3. In order to interpret these results, one genetic system model controlling recombination that consists of general and local recombination modifiers was proposed. The evolution of dynamic genetic systems that would effectively reduce recombinational load without reducing the advantage of recombination was discussed.