500Chapter 15 •Large-Scale Chromosomal Changesinversion—crossover products are not recovered—butthe reasons are different. In a pericentric inversion, thecentromeres are contained within the inverted region.Consequently, the chromosomes that have engaged incrossing-over separate in the normal fashion, withoutthe creation of a bridge (Figure 15-23). However, thecrossover produces chromatids that contain a duplica-tion and a deletion for different parts of the chromo-some. In this case, if a gamete carrying a crossoverchromosome is fertilized, the zygote dies because ofgene imbalance. Again, the result is that only non-crossover chromatids are present in viable progeny.Hence, the RF value of genes within a pericentric in-version is also zero.Inversions affect recombination in another way,too. Inversion heterozygotes often have mechanicalpairing problems in the region of the inversion. Theinversion loop causes a large distortion that can ex-tend beyond the loop itself. This distortion reduces
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