Physical Mapping of the 45S rDNA and 5S rDNA in the Peanut (Arachis hypogaea L.)

Karyotype analysis of two peanut cultivars,Silihong and Shuhua No.4,was conducted.The Silihong karyotype belonged to 2B and the karyotype formula was 2n=4x=40=38m+2sm(4SAT).The Shuhua No.4 karyotype belonged to 1B and the karyotype formula was 2n=4x= 40=40m(2SAT).The 45S rDNA and 5S rDNA sequences were physically mapped by double color fluorescent in situ hybridization(FISH) on the mitotic metaphase chromosomes of the two cultivars.The results showed six pairs of 45S rDNA loci on A2L,A7S,A9L,B3L,B7S,and B8L(A and B stand for genomes A and B respectively,L and S represent chromosome long and short arms,and the numbers indicate chromosomes serial number),as well as two pairs of 5S rDNA loci on A3S and B3S in Silihong,and five pairs of 45S rDNA loci on A2L,A9L,B3L,B7S,and B9L,as well as two pairs of 5S rDNA loci on A3S and B3S in Shuhua No.4.The FISH results showed that the chromosomal locality of 5S rDNA was relatively conservative,while that of 45S rDNA was variable in the peanut.