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Crossing-over

H. L. K. Whitehouse
Science Progress (1933-)
Vol. 53, No. 210 (April 1965), pp. 285-296
Stable URL: http://www.jstor.org/stable/43425622
Page Count: 12
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Crossing-over
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Abstract

Crossing-over has been found to be associated with a number of remarkable phenomena: gene conversion, post-meiotic segregation, polarized recombination, and negative interference. The copy-choice hypothesis has proved inadequate as an explanation. A hybrid DNA model of crossing-over is preferred, based on breakage of nucleotide chains at predetermined points in the chromosome, and rejoining by base pairing. Post-meiotic segregation would then be due to the inclusion of a site of mutation in the hybrid region, giving mispairing of bases in the DNA. Gene conversion is attributed to the enzymic correction of such mispairing, and negative interference to such correction and to its association with the hybrid DNA segments within a cross-over. Existing data suggest that the segments, or polarons, delimited by the initial breakage-points, correspond to cistrons. This would mean that crossing-over can be initiated only between genes and not within them.

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