KARYOTYPE AND GENOME SIZE

Although a few cases of natural occurring triploids have been mentioned in the literature (Butorina, 1993; Naujoks et al., 1995; Dzialuk et al., 2007), oaks are diploid species bearing 2n=24 chromosomes. Extra chromosome 2n=24+1,2 or 3 extra chromosomes have been reported as consequences of irregular segregation in mitoses (Zoldos et al., 1998). Reported karyotype studies in Quercus, Lithocarpus, Castanopsis and Castanea (Mehra et al. 1972), and in Quercus (D’Emerico et al. 1995), and Fagus (Ohri and Ahuja 1990, 1991) indicate that the number of chromosomes within the Fagaceae family as a whole is remarkably stable (2n=24).

The reported values of 2C DNA content between oak species vary from 1.17 pg (Q. velutina) to 2.00 pg (Q. coccifera and Q. suber). Species that were investigated include representatives of all three major sections (12 species in Erythrobalanus (red oaks), 12 species in Lepidobalanus (white oaks), 4 species in Cerris). The average 2C DNA contents were 1.81 pg for section Cerris, 1.75 pg for section Lepidobalanus, and 1.56 pg for section Erythrobalanus (Kremer et al., 2007, and table attached). The two oak species with largest genomes, Q. coccifera and Q. ilex (2.00 pg), are both evergreen species and are part of a disputed botanical group (subgenus named Sclerophyllodrys, according to Schwarz (1964)), but are in two different sections in Camus classification (Q. ilex in section lepidobablanus and Q. coccifera in section cerris). This is intriguing, given that molecular phylogenetic analysis separates the evergreen species from the two sections of deciduous oaks (Manos and Steele 1997 and Xu 2004) confirming their earlier subdivision in Sclerophyllodrys by Schwarz (1964).

2C DNA values in related genera are at the lower limits of the range of values observed in oaks: 1.62 pg for Castanea and 1.17 pg for Fagus


DNA CONTENT

GENOME

References

Butorina AK (1993) Cytogenetic study of diploid and spontaneous triploid oaks, Quercus robur L. Ann Sci For 50, Suppl 1:144s-150s

Camus, A. 1936-1954. Les chênes, Monographie du genre Quercus et Monographie du genre Lithocarpus. Encyclopédie Economique de Sylviculture. Vol. VI, VII, VIII. Editions Lechevalier (Paris)

D’emerico S, Bianco P, Medagli P, Schirone B (1995) Karyotype analysis in Quercus ssp. (Fagaceae). Silvae genetica 44: 66-70

Dzialuk A, Chybicki I, Welc M, Sliwinska E, Burczyk J. 2007. Presence of triploids among oak species. Annals of Botany 99 : 959-964  
 
Favre JM, Brown S (1996) A flow cytometric evaluation  of the nuclear content and GC percent in genomes of European oak species. Ann Sci For 53: 915-917

Gallois A, Burrus M, Brown S (1999) Evaluation of DNA content and GC percent in four varieties of Fagus sylvatica L. Ann For Sci 56: 615-618

Kremer, A., M. Casasoli, T. Barreneche, C. Bodénès, P. Sisco, T. Kubisiak, M. Scalfi, S. Leonardi, E.G. Bakker, J. Buiteveld, J. Romero-Severson, K. Arumuganathan, J. Derory, C. Scotti-Saintagne, G. Roussel, M.E. Bertocchi, C. Lexer, I. Porth, F. Hebard, C. Clark, J. Carlson, C. Plomion, H. Koelewijn, and F. Villani. 2007. Fagaceae: comparative Genetic Mapping in Fagaceae. P. 161-187 in “Genome Mapping & Molecular Breeding. Vol. 5: Forest Trees”, Kole, C.R. (ed.). Springer-Verlag, Berlin, Heidelberg, New York, Tokyo

Manos PS and Steele KP (1997) Phylogenetic analyses of “higher” Hamamelidiae based on plastid sequence data. Amer J Bot 84:1407-1419

Xu LA (2004) Diversité de l’ADN chloroplastique et relations phylogénétiques au sein des Fagacées et du genre Quercus. Thèse Université Henri Poincaré, Nancy, 129 pages

Mehra PN, Hans AS, Sareen TS (1972) Cytomorphology of Himalayan Fagaceae. Silvae Genetica 21:102-109

Naujoks G, Hertel H, Ewald D (1995) Characterisation and propagation of an adult triploid pedunculate oak (Quercus robur). Silvae genetica 44: 282-286

Ohri D, Ahuja MR (1990) Giemsa C-banding in Quercus L. (oak) Silvae Genetica 39: 216-219

Ohri D, Ahuja MR (1991) Giemsa C-banding in Fagus sylvatica L., Betula pendula Roth and Populus tremula L.. Silvae Genetica 40: 72- 5

Schwarz O (1964) Quercus L. In: Tutin TG, Heywood VH, Burges NA, Valentine DH, Walters SM  and Webb  DA (eds) Flora Europaea, vol. 1: Lycopodiaceae to Platanaceae, pp. 61-64. Cambridge University Press, Cambridge

Zoldos V, Papes D, Brown SC, Panaud O, Siljak-Yakovlev S (1998) Genome size and base composition of seven Quercus species: inter- and intra- population variation. Genome 4:162-168