Cytological study of Rubenstrema exasperatum (Trematoda:Omphalometridae).

Cytological studies on Rubenstrema exasperatum were carried out. The number of chromosomes in diploid cells (2n = 16), and the morphological characteristics of the karyotype were determined. All the chromosomes (from Nos 2 to 8) had a well-defined short arm and, in accordance with the Ic values, were determined to be meta-submetacentric. Polymorphism was established in the length of the 2 homologues of the 1st chromosome. This pair is probably linked with sex determination.

Meiosis and some aspects of cytological mechanisms of chromosomal sex determination in nematode species.

Meiotic division in Toxascaris leonina, Baylisascaris transfuga, Hexametra sp., Toxocara canis, T. cati, Heterakis gallinarum and Physaloptera clausa of the class Nematoda were studied. Chromosomal sex determination type in different taxa is described. The XX-XO type of sex determination predominates in the species examined. A Y chromosome occurs only in B. transfuga. A correlation between the number and length of sex chromosomes and autosomes in the different taxa was established.

Cytological studies on three hymenolepidid species.

The karyotypes of Vampirolepis nana, Hymenolepis diminuta and Vampirolepis erinacei (Cestoda: Cyclophyllidea) have been described. The number of chromosomes in the diploid cell of the studied taxa was 2n = 12. The absolute and the relative lengths of the chromosomes of V. nana and H. diminuta were measured. The chromosomes had similar metric values. In the karyotypes of V. nana and H. diminuta there were ten one-arm chromosomes and one two-arm chromosome (the third in length in the karyotype of V. nana and the first in length in the karyotype of H. diminuta). The chromosomes in the karyotype of V. erinacei had one arm which was proved by the terminal localization of the constitutive heterochromatin. The examined species differed in the morphology of some chromosomes in the karyotypes.

The karyotype of four Trichinella species.

Karyological studies of Trichinella spiralis, T. pseudospiralis, T. nativa and T. nelsoni were undertaken. Comparison of the karyotypes of these Trichinella species showed that the chromosome number of all four species is 2n = 6 for female specimens and 2n = 5 for males. The differences found in the relative chromosome lengths of the individual Trichinella species are not significant. Centromeric index data indicate that T. nativa and T. spiralis have similar centromere dispositions and differ from the other two species by the disposition of the centromere of the first submetacentric chromosome pair. In T. nativa and T. nelsoni the univalent sex chromosome is the second in size. It is slightly submetacentric chromosome, while in T. spiralis and T. pseudospiralis it is the third metacentric chromosome. The data from the karyological investigations may be used as additional karyosystematic characteristics when differentiating the Trichinella species studied.

Comparative cytological studies of mitotic and male meiotic karyotype of Ascaridia dissimilis (Vigueras, 1931) and Ascaridia galli (Schrank, 1788).

Gametogony and spermatogenesis of A. dissimilis and A. galli were studied. It was found that the chromosome number of A. dissimilis is 2n = 10 for female specimens and 2n = 9 for male ones. The chromosome number of A. galli is also 2n = 10 for female specimens and 2n = 9 for males ones. Comparison of the relative length of chromosomes in the chromosome set, expressed in percentages, shows nearly equal magnitudes for both species. Spermatogenesis processes were studied. It was found that they run a similar course in both species. In the following stages of gametogony and spermatogenesis differences between the two species are not discovered.

On the karyotype of a laboratory Trichinella strain from Bulgaria.

The karyotype of male and female individuals of the species Trichinella nelsoni was studied. It was found that the number of chromosomes in females individuals is 2n = 6 and in males 2n = 5. Each pair of chromosomes differs from one another as to dimensions and location of the centromere. The univalent chromosome that was found in the chromosome set containing five chromosomes is the second largest submetacentric chromosome. It is suggested that this chromosome is the sex chromome of the studied Trichinellae.

Morphology and behaviour of sex chromosomes during meiosis in Ascaris suum.

The morphology and behaviour of sex chromosomes was studied in A. suum during meiosis. It was found that the five sex chromosomes have their proper characteristic. The largest is submetacentric, of 2 microns mean length. The second largest is acrocentric, mean length of 1.4 mu. The third largest is metacentric, 1.2 mu mean length. The fourth and the fifth are metacentric, of mean length of 1 mu. In primary and secondary spermatocyte cells the sex chromosomes are close to each other, most often in the peripheral part of the cell. During anaphase I the pentad sex chromosomes lie freely between the two sister cells. It is assumed that in anaphase II the five sex chromosomes divide equally and are regularly distributed in the daughter cells. It was found that the chromosomes set of female Ascaris in metaphase I contains 24 bivalent chromosomes n = 24 and of male Ascaris 19 bivalents and 5 univalents. It is assumed that the univalent chromosomes, found in spermatocyte cells, determine sex.