Introduction to Genetic Analysis 501

Introduction to Genetic Analysis 501 - 44200_15_p481-520...

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500 Chapter 15 Large-Scale Chromosomal Changes inversion—crossover products are not recovered—but the reasons are different. In a pericentric inversion, the centromeres are contained within the inverted region. Consequently, the chromosomes that have engaged in crossing-over separate in the normal fashion, without the creation of a bridge (Figure 15-23). However, the crossover 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 crossover chromosome is fertilized, the zygote dies because of gene 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 mechanical pairing problems in the region of the inversion. The inversion loop causes a large distortion that can ex- tend beyond the loop itself. This distortion reduces
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