Practice question

In inversion heterozygotes, normal and inverted chromosomes form an inversion loop at pachytene to maximize homology pairing. A single crossover inside the loop exchanges segments but produces unbalanced chromatids: duplicated outside regions with deletions, plus in paracentric cases dicentric chromatid and acentric fragment that cause breakage or loss. Most recombinant products are inviable, so recovered progeny show only parental nonrecombinant chromosomes, giving apparent suppression of recombination. This property preserves coadapted gene complexes and is used as balancer chromosomes in Drosophila genetics to prevent loss of lethal mutations.