The effect of heterochromatin on synapsis of the sex chromosomes of Peromyscus (Rodentia, Cricetidae). Academic Article uri icon


  • The pairing behavior of the sex chromosomes in male and female individuals representing seven species of Peromyscus was analyzed by electron microscopy of silver-stained zygotene and pachytene configurations. Six species possess submetacentric or metacentric X chromosomes with heterochromatic short arms. Sex-chromosome pairing in these species is initiated during early pachynema at an interstitial position on the X and Y axes. Homologous synapsis then progresses in a unidirectional fashion towards the telomeres of the X short arm and the corresponding arm of the heterochromatic Y chromosome. The distinctive pattern of synaptic initiation allowed a late-synapsing bivalent in fetal oocytes to be tentatively identified as that of the X chromosomes. In contrast to the other species, Peromyscus megalops possesses an acrocentric X chromosome and a very small Y chromosome. Sex-chromosome pairing in this species is initiated at the proximal telomeric region during late zygonema, and then proceeds interstitially towards the distal end of the Y chromosome. These observations suggest that the presence of X short-arm heterochromatin and corresponding Y heterochromatin interferes with late-zygotene alignment of the pairing initiation sites, thereby delaying XY synaptic initiation until early pachynema. The pairing initiation sites are conserved in the vicinity of the X and Y centromeres in Peromyscus, and consequently the addition of heterochromatin during sex-chromosome evolution essentially displaces these sites to an interstitial position.

published proceedings

  • Cytogenet Cell Genet

author list (cited authors)

  • Hale, D. W., Hedin, M. C., Smith, S. A., Sudman, P. D., & Greenbaum, I. F.

citation count

  • 18

complete list of authors

  • Hale, DW||Hedin, MC||Smith, SA||Sudman, PD||Greenbaum, IF

publication date

  • January 1991