Allium chromosome evolution and DNA sequence localization.

Background: Molecular cytogenetics, utilizing DNA probes, serves as a critical tool for mapping genes to the physical structures of chromosomes.

Methods: In this study, we examined three Allium species: A. cepa L., A. sativum L., and A. fistulosum L., using in situ hybridization to localize 45S rDNA and 5S rDNA genes.

Results: We observed variation in both the chromosomal localization and signal intensity of the 45S and 5S rDNA probes across the species. Notably, in A. sativum, additional 5S rDNA signals were detected on chromosome 8, in a heterozygous condition. Additionally, we aimed to explore the feasibility of localizing genes associated with pigment biosynthesis in A. cepa, specifically the PAL and FLS genes. For this, we employed TSA-FISH on both meiotic and mitotic chromosomes. Preliminary results suggested that the PAL gene was localized to meiotic metaphase chromosomes, while the single-copy FLS gene was detected on mitotic chromosomes.

Conclusion: The TSA-FISH technique proved neither routine nor robust for consistent localization of these specific probes in plant chromosomes. The findings based on rDNA analysis also offer insights into potential evolutionary implications among the different Allium species studied.