The 2L telomere in polytene chromosomes of the Tel¹ strain shows a difference in morphology compared to Oregon-R; the 21B1 band appears slightly decondensed and the 21A region is considerably longer than that in Oregon-R. The expanded 21A region has two morphologically distinct parts; a light proximal zone and a denser distal zone, which sometimes has a granular appearance and occasionally appears to have a banded structure.

The polytene chromosomes of the Gaiano-O stock (which contains the Tel¹ factor on the third chromosome) have long telomeric regions which are often associated with each other. The third chromosome of the Gaiano-O stock (which contains the Tel¹ factor on the third chromosome) has been crossed into the Oregon-R background and the stock has been examined after 60 generations. All the major chromosomes have long telomeres, indicating that the Tel¹ factor has caused dramatic growth in the Oregon-R derived telomeres. Tel¹ is correlated with increased addition of HeT-A and TART-elements to chromosome ends and telomere elongation.