Final answer:
During prophase I, the four chromatids do not separate from each other because of the synaptonemal complex and cohesin proteins, which hold the homologous chromosomes together. The synaptonemal complex ensures alignment and allows for genetic recombination.
Step-by-step explanation:
The four chromatids do not separate from each other during prophase I because they are held together by a protein lattice called the synaptonemal complex and by cohesin proteins at the centromere. This tight pairing of the homologous chromosomes is called synapsis. The synaptonemal complex ensures that the homologous chromosomes stay aligned and allows for genetic recombination to occur between maternal and paternal chromosomes.