Influence of chromosomal gene position on intragenic recombination in maize

Chromosome interchanges were used to relocate four alleles of the wx locus in order to analyze the distribution of recombination potential of the maize genome. There are two homotranslocation series: proximal, interchanges proximal to wx, thus moving the wx locus to varied positions away from a centromere; and distal, interchanges distal to wx, thereby lengthening the segment distal to wx. 1. Among the controls (homoalleles on standard chromosomes), derived from outcrosses (heterozygous sources), yield more recombination than these combinations in inbred lines. 2. All heteroallelic, homotranslocation combinations, irrespective of the extent of the locus-centromere distance, are equal or less in recombination frequency than the wx recombination in the standard chromosome. 3. Among all heteroalleles on homotranslocations, there is a positive linear correlation of inter-allelic recombination with increasing distance from a centromere but the value is always less than found in the standard chromosomes. This also is true for the same heteroallele at different positions; the longer distances show a higher recombination value than the shorter wx-centromere distance. 4. There is no effect of a lengthening distal segment on wx interallelic recombination. 5. The frequencies of Wx pollen grains arising from homoalleles on homotranslocations in most instances (except for 90/90) are not significantly different from the frequencies found with standard chromosomes. 6. The reversion frequency of the same homoallele at different positions has no relationship with the wx-centromere or wx-breakage-point distance. 7. Different homoalleles at the same position are not equally affected in wx reversion rate at the new position, although no trend is evident in wx-centromere or wx-breakage-point distance. 8. The most variation in percentage change of the Wx frequency from the controls among different heteroalleles with the same homotranslocation is found among interchanges with relatively short wx-breakage-point distances. 9. There is a significant environmental effect; the greatest change between years is among the heteroalleles with higher wx recombination. 10. Homoalleles differ from heteroalleles in response to various factors, such as wx-centromere and wx-breakage-point distances. This supports the expectation that Wx pollen grains arising from homoalleles have a different origin than do Wx pollen grains arising from heteroalleles.