Crossing over Transitional Reasoning Download PDF

Questions

1. 1.

   A geneticist investigates two germ cells undergoing meiosis in an organism with the heterozygous genotype AB/ab, where genes A and B are linked on the same chromosome pair. In Cell 1, meiosis proceeds with no crossing over between these loci, whereas in Cell 2, a single crossover event occurs between non-sister chromatids in the region between gene A and gene B. Based on this investigation, which comparison accurately evaluates the resulting gametes and the biological significance of crossing over?

   • A) Cell 1 generates greater genetic diversity because crossing over disrupts the balanced segregation of homologous pairs during anaphase I.
   • B) Cell 1 produces only parental-type gametes (AB and ab), whereas Cell 2 produces both parental (AB, ab) and recombinant (Ab, aB) gametes, demonstrating that crossing over generates novel allele combinations without altering gene loci.
   • C) Cell 2 produces exclusively recombinant gametes (Ab and aB) because a crossover event reciprocally alters all four chromatids within the homologous tetrad.
   • D) Cell 2 creates novel alleles that did not exist in either parent chromosome, demonstrating that crossing over acts as a mutagenic process rather than a genetic reshuffling mechanism.