Meiosis and Sources of Genetic Variation (1C) Practice Test

In a population study of wild Drosophila melanogaster, investigators crossed females heterozygous for two linked markers on chromosome 2 (A and B) with males homozygous recessive (ab/ab). Female germ cells were exposed to a brief heat pulse during early prophase I, a condition previously associated with increased double-strand break formation. Offspring were scored for parental (AB, ab) versus recombinant (Ab, aB) phenotypes. Across replicates, the recombinant fraction increased from 8% (control) to 18% (heat pulse), while total offspring number was unchanged.

Which outcome is most likely due to crossing over during meiosis in the heat-pulse group?

In an experimental observation of Arabidopsis male meiosis, researchers introduced a fluorescent reporter that marks a specific chromosomal interval flanked by two polymorphic sites. Meiocytes were isolated and the interval was sequenced from individual haploid microspores. Compared with a control line, a mutant line showed a marked reduction in microspores carrying mixed combinations of the flanking polymorphisms, while overall viability and chromosome number appeared normal. Which interpretation is most consistent with meiosis processes in the mutant line?