Structure of and homology between pachytene and somatic metaphase chromosomes of the tomato

The pachytene and somatic metaphase chromosomes of tomato are structurally differentiated into proximal chromatic and distal achromatic parts. The pachytene chromosomes have very clear and characteristic chromosome markers, with the help of which all 12 bivalents can be clearly identified. Based on the size, the arm ratio, the ratio of chromatic parts and the presence and size of achromatic parts, all 12 pairs of somatic chromosomes can also be identified, and each pair be homologised with the corresponding pachytene bivalent. A comparison of the lengths of chromatic and achromatic parts of pachytene chromosomes with the chromatic and achromatic parts of the corresponding somatic chromosomes indicate, that, on an average, the chromatic parts are contracted by a factor of 4 to 5, whereas the achromatic parts are contracted by a factor of 30. The heteropycnosis near the centromere in tomato chromosomes therefore is not a special characteristic of meiotic chromosomes, but present in somatic metaphase chromosomes also.This study was part of a project resulting from a contract between the AssociationEuratom-I.T.A.L. and the Agricultural University of Wageningen.