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11 Two gametes contain wild-type nonrecombinant chromosomes.

Nonrecombinant gamete with paracentric inversion __

The other two contain recombinant chromosomes that are missing some genes; these gametes will not produce viable offspring.

Conclusion: The resulting recombinant gametes are nonviable because they are missing some genes.

not viable and thus no recombinant progeny are observed. Let's see why this occurs.

FIGURE 9.13 illustrates the results of crossing over within a paracentric inversion. The individual is heterozygous for an inversion (see Figure 9.13a), with one wild-type, unmutated chromosome (AB^CDEFG) and one inverted chromosome (AB^EDCFG). In prophase I of meiosis, an inversion loop forms, allowing the homologous sequences to pair up (see Figure 9.13b). If a single crossover takes place in the inverted region (between segments C and D in Figure 9.13), an unusual structure results (see Figure 9.13c). The two outer chromatids, which did not participate in crossing over, contain original, nonrecombinant gene sequences. The two inner chromatids, which did cross over, are highly abnormal: each has two copies of some genes and

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