Introduction to Genetic Analysis 500

Introduction to Genetic Analysis 500 - 44200_15_p481-520...

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499 15.2 Changes in chromosome structure able. Hence, a crossover event, which normally generates the recombinant class of meiotic products, is instead lethal to those products. The overall result is a drastically lower frequency of viable recombinants. In fact, for genes within the inversion, the RF is close to zero. (It is not exactly zero because double crossovers involving only two chromatids—which are rare—are viable.) For genes flanking the inversion, the RF is reduced in pro- portion to the size of the inversion, because for a longer inversion, there is a greater probability of a crossover oc- curring within it and producing an inviable meiotic product. In the case of a heterozygous pericentric inversion, the net genetic effect is the same as that of a paracentric Most analyses of inversions are carried out on diploid cells that contain one normal chromosome set plus one set carrying the inversion. This type of cell is called an inversion heterozygote, but note that this des-
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