Interstitial Telomeric Repeats Are Rare in Turtles.

Area of Science:

• Genomics
• Cytogenetics
• Evolutionary Biology

Background:

• Telomeres protect chromosome ends in eukaryotes.
• Interstitial telomeric repeats (ITRs) are telomeric sequences found at non-telomeric chromosomal locations.
• Understanding ITR distribution provides insights into genome evolution and chromosomal stability.

Purpose of the Study:

• To map the distribution of (TTAGGG)n telomeric repeats in turtle karyotypes.
• To investigate the occurrence and origins of interstitial telomeric repeats (ITRs) in turtles.
• To compare ITR prevalence in turtles with other reptile groups and birds.

Main Methods:

• Fluorescence in situ hybridization (FISH) was used to map (TTAGGG)n repeats.
• Karyotypes of 30 turtle species from nine families were analyzed.
• Data was combined with existing literature for comparative analysis.

Main Results:

• All 30 turtle species exhibited terminal telomeric repeats at chromosome ends.
• Interstitial telomeric repeats (ITRs) were detected in only five species across three families.
• Seven independent origins of ITRs were inferred, primarily in centromeric positions.
• ITR distribution did not directly correlate with interchromosomal rearrangements.

Conclusions:

• Centromeres and non-recombining sex chromosome regions are dynamic in turtles.
• The rarity of ITRs in turtles aligns with generally low rates of chromosomal rearrangement.
• Despite a slow-evolving reputation, turtles exhibit genomic dynamism in specific regions.