Cytological Features Of Peanut Genome

This chapter aims to update the chromosomal features evaluated by classical and molecular cytogenetic techniques. Karyotype variability detected within and among species was very useful to unravel the taxonomy of the genus and to establish relationships among species. This chapter includes analyses of chromosome morphology, heterochromatin, rDNA loci, as well as dispersed and clustered repetitive sequences. A critical review of the genome sizes of Arachis species is also provided. The usefulness of chromosome data is presented in three examples. The first one deals with the origin of the cultivated peanut. Molecular cytogenetics evidenced that the varieties of A. hypogaea may have had a single genetic origin, that A. monticola is a direct tetraploid ancestor of peanut, and that A. duranensis (A genome) and A. ipaensis (B genome) are the diploid progenitors of the AABB tetraploids. The second one pointed to the analysis of the origin of the rhizomatous tetraploids and their relation to the unique diploid species (A. burkartii) of section Rhizomatosae. The cytogenetic data suggest that A. burkartii has to be discarded as a genome donor of the tetraploids, and that the latter may have had independent origins involving different species. The third one concerns the species of section Arachis, and how the chromosome data aided in the establishment of the genome groups (A, B, D, F, G, and K).