Most spiders exhibit a multiple sex chromosome system, X(1)X(2)0, whose origin has not been satisfactorily explained. Examination of the sex chromosome systems in the spider genus Malthonica (Agelenidae) revealed considerable diversity in sex chromosome constitution within this group. Besides modes X(1)X(2)0 (M. silvestris) and X(1)X(2)X(3)0 (M. campestris), a neo-X(1)X(2)X(3)X(4)X(5)Y system in M. ferruginea was found. Ultrastructural analysis of spread pachytene spermatocytes revealed that the X(1)X(2)0 and X(1)X(2)X(3)0 systems include a pair of homomorphic sex chromosomes. Multiple X chromosomes and the pair exhibit an end-to-end pairing, being connected by attachment plaques. The X(1)X(2)X(3)X(4)X(5)Y system of M. ferruginea arose by rearrangement between the homomorphic sex chromosome pair and an autosome. Multiple X chromosomes and the sex chromosome pair do not differ from autosomes in a pattern of constitutive heterochromatin. Ultrastructural data on sex chromosome pairing in other spiders indicate that the homomorphic sex chromosome pair forms an integral part of the spider sex chromosome systems. It is suggested that this pair represents ancestral sex chromosomes of spiders, which generated multiple X chromosomes by non-disjunctions. Structural differentiation of newly formed X chromosomes has been facilitated by heterochromatinization of sex chromosome bivalents observed in prophase I of spider females.

Laboratory of Arachnid Cytogenetics Department of Genetics and Microbiology Faculty of Science Charles University Prague Vinicná 5 CZ 128 44 Prague 2 Czech Republic

See more in PubMed

Heredity (Edinb). 1948 Jun;2(Pt 1):77-100 PubMed

J Cell Sci. 1982 Dec;58:411-22 PubMed

Chromosoma. 1993 Jan;102(2):71-80 PubMed

Comp Biochem Physiol. 1961 Apr;2:241-89 PubMed

Genome. 2001 Apr;44(2):172-84 PubMed

Chromosoma. 1984;90(1):50-6 PubMed

Chromosoma. 1981;82(1):41-53 PubMed

Exp Cell Res. 1972 Nov;75(1):304-6 PubMed

Chromosome Res. 2006;14(8):859-80 PubMed

Braz J Biol. 2005 May;65(2):193-202 PubMed

Chromosoma. 1980;77(1):69-81 PubMed

Biol Rev Camb Philos Soc. 1990 Aug;65(3):249-76 PubMed

Hereditas. 2006 Dec;143(2006):123-9 PubMed

Advances in Understanding the Karyotype Evolution of Tetrapulmonata and Two Other Arachnid Taxa, Ricinulei and Solifugae

Insights into the Karyotype Evolution of Charinidae, the Early-Diverging Clade of Whip Spiders (Arachnida: Amblypygi)

Evolutionary pattern of karyotypes and meiosis in pholcid spiders (Araneae: Pholcidae): implications for reconstructing chromosome evolution of araneomorph spiders

Patterns of Sex Chromosome Differentiation in Spiders: Insights from Comparative Genomic Hybridisation

Insights into the karyotype and genome evolution of haplogyne spiders indicate a polyploid origin of lineage with holokinetic chromosomes

Dynamic karyotype evolution and unique sex determination systems in Leptidea wood white butterflies