Chromosome morphology, number and behavior of some Arizona Plantago species

Abstract

Mitosis and meiosis of five Plantago species were analyzed. Plantago argyrea, P. patagonica and P. wrightiana contain 2n = 20 chromosomes and P. rhodosperma and P. virginica 2n = 24 chromosomes. Similar modes of evolution of the karyotypes of the 2n = 20 species are suggested. All species are presumed to be tetraploid, arising from 2n = 10 and 2n = 12 ancestors. Structural changes in the karyotype of 2n = 12 species could produce one or more large chromosomes resulting in a decrease in chromosomes from 6 to 5. Consequently, chromosome lengths in 2n = 10 and derived 2n = 20 species could be increased by addition of repetitive DNA along the length of each chromosome to maintain chromosome field. Chromosomes of 2n = 24 species are more symmetrical and presumably more primitive than the 2n = 20 species. Chiasma frequencies in meiotic cells of all five species are similar. This suggests that the majority of changes DNA content are in repetitive DNA.