The mice from the vicinity of Olympia in northwestern Peloponnesus were homozygous for eight Robertsonian translocations: Rb 1. Finally, the mice from Thebes were homozygous for translocations Rb 2. They were homo- or heterozygous for Rb 6. Mitotic and meiotic testicular cells of Nesticodes rufipes stained with Giemsa. After silver impregnation, mitotic metaphase cells of A. The number of active NORs varied from two to six per cell Figure 4a ,b. Mitotic cells of Argyrodes elevatus a-b and Nesticodes rufipes c-d after Giemsa staining a and c and silver nitrate impregnation b and d.
The chromosomal characteristics observed in A. Theridiidae and its sister-group Nesticidae constitute the theridioids, a derived branch within the Araneoidea clade Griswold et al. It appears thus that the main trend of chromosome evolution within Araneoidea was the reduction of the diploid number with the conservation of the sex chromosome system.
This hypothesis is reinforced by the fact that the X chromosome of A. An alternative mechanism would be the addition of constitutive heterochromatin. The presence of metacentric or submetacentric chromosomes such as observed in A.
Nevertheless, the mechanism of pericentric inversions observed in A. The karyotype of most N. However, the mitotic and meiotic cells of one adult male showed two extra chromosomes. The diploid number variation in this individual was certainly not due to chromosome fission as the chromosomes were of uniform size, i. Taking into account that the extra chromosome pair was seen in all cells of this individual, it is possible to infer that it originated by a meiotic non-disjunction during the formation of the maternal or paternal gametes.
Alternatively, considering the haploid numbers verified in the metaphase II nuclei, this extra chromosome pair could correspond to B chromosomes with a regular meiotic behavior following a Mendelian transmission rate. There are no previous records on the NOR distribution pattern in theridiid spiders in the literature.
Nucleolar organizer regions on autosomes, such as those observed in A. Although the two theridiids exhibited great karyotypic differences, it is interesting to note that both species showed NORs on the terminal regions of one medium-sized autosomal pair pair 4.
The analysis of a larger number of Theridiidae spiders could reveal if NORs on medium-sized autosomal elements are a shared feature of the family. The increase of NORs numbers in A. In Oxyopidae spiders Entelegynae , we also observed a relationship between a large number of NORs and an extremely derived karyotype.
Associate Editor: Yatiyo Yonenaga-Yassuda. National Center for Biotechnology Information , U. Journal List Genet Mol Biol v. Genet Mol Biol. Published online Dec 1. Author information Article notes Copyright and License information Disclaimer. Corresponding author. Send correspondence to Marielle C.
E-mail: rb. Received Feb 23; Accepted May This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article has been cited by other articles in PMC. Abstract Theridiidae is a derived family within the Araneoidea clade. Keywords: chromosome morphology, cytogenetic, meiosis, nucleolar organizer region, sex chromosome system. Introduction Theridiidae is among the largest families of the order Araneae, including 2. Material and Methods The sample of 58 individuals analyzed in this work comprised: A. However, the allele Q of a gene on a separate chromosome is results in a gray color irrespective of the genotype of the "B" gene q has no effect on color.
Circle the correct letter. The R and S genes loci are 20map units 20 cM apart. Assign phenotypes "r s" "R S" "R s" and "r S". Biology , Sample Transmission Genetics Problems 1. In a dihybrid the genes are located on different chromosomes. Which of the following diagrams does not represent a stage of meiosis in this organism?
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