49915.2 Changes in chromosome structureable. Hence, a crossover event, which normally generatesthe recombinant class of meiotic products, is insteadlethal to those products. The overall result is a drasticallylower frequency of viable recombinants. In fact, forgenes within the inversion, the RF is close to zero. (It isnot exactly zero because double crossovers involvingonly two chromatids—which are rare—are viable.) Forgenes ﬂanking the inversion, the RF is reduced in pro-portion to the size of the inversion, because for a longerinversion, there is a greater probability of a crossover oc-curring within it and producing an inviable meioticproduct.In the case of a heterozygous pericentricinversion, thenet genetic effect is the same as that of a paracentricMost analyses of inversions are carried out ondiploid cells that contain one normal chromosome setplus one set carrying the inversion. This type of cell iscalled an inversion heterozygote,but note that this des-
This is the end of the preview. Sign up
access the rest of the document.