Final answer:
The observation of gametes receiving one copy of each homologous chromosome pair during meiosis explains Mendel's law of segregation, detailing how alleles segregate into gametes.
Step-by-step explanation:
The observation that gametes receive one copy of each pair of homologous chromosomes and one copy of the sex chromosomes during meiosis is a physical manifestation of Mendel's law of segregation. This law details how genes for specific traits are distributed to gametes. When gametes form, the two alleles for each gene—located on homologous chromosomes—segregate so that each gamete carries only one allele for each gene. This process restores the diploid state during fertilization when two gametes merge, bringing together one allele from each parent.
The accurate answer to the question is: while studying meiosis, you observe that gametes receive one copy of each pair of homologous chromosomes and one copy of the sex chromosomes. This observation is the physical explanation of Mendel's law of segregation. When homologous chromosomes with their different versions of each gene are segregated into daughter cells during meiosis, this is what accounts for the law of segregation and is crucial for the accurate prediction of offspring genotypes using tools like the Punnett square.