Final answer:
Mendel's law of segregation is best explained by the separation of homologous chromosomes during anaphase I of meiosis, where each gamete receives one chromosome from each pair.
Step-by-step explanation:
The aspect of chromosome behavior that most clearly accounts for Mendel's law of segregation is the movement of homologous chromosomes to opposite poles at anaphase I of meiosis. During this phase, the pairs of homologous chromosomes are separated, ensuring that each gamete contains only one chromosome from each pair. This separation is critical for producing gametes with a single set of chromosomes (haploid), and it is the foundation for the concept that each parent contributes one allele for every gene.
In contrast, the movement of sister chromatids to opposite poles occurs during anaphase II of meiosis II, after each chromosome has already been separated into different gametes. Therefore, it does not contribute directly to Mendel's law of segregation.
The aspect of chromosome behavior that most clearly accounts for Mendel's law of segregation is the movement of sister chromatids to opposite poles at anaphase II of meiosis. During anaphase II, the sister chromatids, which are genetically identical, separate and move to opposite ends of the cell. This ensures that each resulting gamete receives only one copy of each chromosome, as predicted by Mendel's law of segregation.