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

In a fish species, researchers tracked two unlinked loci using barcoded sequencing of single sperm. They observed that each sperm carried exactly one allele at each locus and that the combination of alleles across loci varied widely among sperm from the same male. No evidence suggested recombination within either locus region. How does independent assortment best explain the observed sperm-to-sperm variation?

A) It produces different allele combinations by random distribution of maternal and paternal homologs into haploid gametes

B) It produces different allele combinations by exchanging DNA segments between sister chromatids

C) It produces different allele combinations by introducing random point mutations during cytokinesis

D) It produces different allele combinations by copying one homolog twice and discarding the other

A mouse spermatocyte line was engineered so that a pair of homologous chromosomes carries distinguishable centromere tags (red vs blue) and a distal arm marker (green vs yellow). Live-cell imaging showed random orientation of the red and blue homologs at the meiosis I spindle, while no crossing over was detectable on that chromosome pair. Which statement best describes how independent assortment contributes to genetic diversity in the resulting sperm?

A) It generates new allele combinations only when a crossover occurs between the distal markers

B) It randomizes which homolog (red-green vs blue-yellow) enters each haploid cell at meiosis I

C) It randomizes separation of sister chromatids at meiosis I, producing recombinant chromatids

D) It ensures that all sperm receive both homologs to maintain diploidy