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Chromosomes of two diploid (2n = 2x = 16) subspecies of Medicago sativa ssp. caerulea and ssp. falcata and their hybrid were studied by C-banding. This study was undertaken to improve the C-banding technique for alfalfa chromosomes, develop a C-banded karyotype of the ssp. caerulea and ssp. falcata, and determine if the same C-banding technique could be used to identify parental chromosomes in hybrids. The chromosomes of ssp. falcata have only centromeric bands and thus individual chromosomes could not be identified. One accession of ssp. falcata displayed an interstitial band in the middle of the long arm on the satellite chromosome. However, chromosome-specific bands were observed in ssp. caerulea enabling the identification of each of the eight pairs of chromosomes and the development of a idiogram. All chromosomes had centromeric bands and a terminal band in the short arm except the satellite chromosome (chromosome 8). Interstitial bands were also observed in the short arms, with the exception of chromosome 7. Chromosomes 1, 2, 3, and 8 each had one prominent interstitial band in their long arm. The satellited chromosome is easy to identify because of the presence of the secondary constriction, two bands located on either side of the nucleolar organizer region, and a large terminal band on its long arm. The differences in banding patterns between these subspecies allowed the identification of parental chromosomes in hybrid cells.

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Barnes et al., 1977). One of these sources A reference karyotype of tetraploid alfalfa (Medicago sativa subsp.

A Giemsa C-banding technique was used to study the amount and location of constitutive heterochromatin in diploid (2n = 2x = 16) Medicago sativa ssp. falcata (L.) Arcangeli. Most accessions had the standard C-banding pattern with centromeric bands on all the chromosomes and a prominent heterochromatic band at the nucleolar organizer regions (NOR) of the satellited (SAT) chromosomes. However, we observed in various accessions that constitutive heterochromatic C-bands can exist at the telomeric ends of all the chromosomes. Interstitial bands occurred on the short arms of all chromosomes except for chromosome 3 and on the long arms of chromosomes 1, 2, 3, and 6, only. Rearranged chromosomes such as isochromosomes have been observed for the short arms of chromosomes 2 and 6. This is the first report on the existence of C-banding polymorphisms and the detection of putative isochromsomes in the chromosomes of diploid ssp. falcata which could have contributed to the variation observed in cultivated alfalfa.