PubMed Health⌕ Search

Biomedical subjects

B F Chadov

Publications and source records attributed to B F Chadov.

29 records · Page 2Linked to original sources
PubMed1994

[Mutagenesis and interchromosomal effect on crossing over in Drosophila].

The possibility of mutational consequences of interchromosomal effect on crossing-over was studied in Drosophila melanogaster females with four genotypes: (1) structurally normal (control); (2) heterozygous at In(1)-Muller-5 inversion (X chromosome); (3) heterozygous at In(3LR)CxD inversion (chromosome 3); and (4) heterozygous at both inversions. The mutational effect was determined through the loss of autosome 2 and formation of arm compounds C(2L) and C(2R). In females with recombinations, the rate of mutational events did not exceed that of the control. It was concluded that interchromosomal effect on crossing-over is of a regulatory character and disturbs neither recombination itself nor chromosome pairing. Coorientation X-3 leading to the appearance of intersexes in the progeny occurred in meiosis in females with two inversions.

Animals↗
PubMed1991

[From the phenomenon of nondisjunction to the problem of chromosome co-orientation (75th anniversary of Bridges' article].

The concepts of the mechanism of chromosome nondisjunction in Drosophila are described in a historical retrospective. Evidences are given for the appropriateness of the term co-orientation in the traditional sense used by geneticists treating nondisjunction. There are 6 variants of co-operation in Drosophila meiosis depending upon the number and particular chromosomes involved in co-orientation. The classical chromosome nondisjunction is a variant of co-orientation in the bivalent composed of two homologous chromosomes. By comparing the different variants of pairing (pairing in bi- and multivalents) resulting in co-orientation, the elementary events preceding co-orientation may be identified. The author reviews his recent data concerning the similarities of the co-orientation of two homologs and the co-orientation of two nonhomologs in Drosophila meiosis. The concept of the role of pairing in the precentromeric heterochromatic region during chromosome co-orientation is considered, and the hypothesis of delayed pairing in this region during meiotic prophase is put forward. Based on the suggested hypothesis clarified are (i) the relationship of pairing, crossing over, and disjunction of homologous chromosomes (ii) the relationship of crossing over and co-orientation of nonhomologous chromosomes, and (iii) the time when the contact resulting in nonhomolog co-orientation takes place.

Animals↗
PubMed1981

Non-homologue pairing and spontaneous meiotic interchanges in Drosophila melanogaster females.

Spontaneous interchange between the X chromosomes and the C(2L) autosomal compound in their centromeric regions was studied in y/XY;C(2L);C(2R) and In(1)dl-49+BM1/XY;C(2L);C(2R) Drosophila melanogaster females. These females were mated with F(2L)/F(2L);C(2R) males. Interchange occurrence was recorded as the appearance of an F1 individual with a half-translocation of either X . 2L or Y . 2L type. 37 interchanges were recovered in y/XY and 67 in In(1)/XY females. The majority of the interchanges were of meiotic origin. The interchanges were mainly C(2L)-XY; the most frequent type of half-translocation was Y . 2L;dl-49+BM1. Inversion increased about 5-fold the interchange frequency. In the course of C(2L)-XY interchange, the other X chromosome and C(2R) compound regularly paired and disjoined. In y/XY females, 8 crossover half-translocations of meiotic origin were recovered. The results obtained indicate that meiotic pairing between the X's and C(2L) occurred in the females examined. According to our estimates, XY-C(2L) pairing is associated with interchange in the heterochromatic centromeric regions with a frequency of 10(-3). The recovery of crossover half-translocations supports the chromocentral model of non-homologous pairing and allows us to assume that a chromosome may simultaneously pair with a homologue and a non-homologue. The disjunction pattern of this trivalent depends on its structure in each particular case. The chromosome-segregation pattern resulting from spontaneous interchanges was similar to that resulting from radiation-induced interchanges in the immature oocytes described by Parker. This similarity suggests that non-homologue pairing occurs in the immature oocytes too. The non-homologue-pairing pattern established by the interchange test conformed well with that previously established in y/XY and In(1)XY females by the distribution test.

Animals↗
PubMedDate not supplied

Disturbed centromeric meiotic pairing leads to chromosome breaks.

In Drosophila females an extended deletion of the second autosome pericentric heterochromatin Df(2R) M-S2-10 under heterozygous conditions results in the loss of autosome 2, formation of autosomal compounds and stable acrocentric chromosomes (free arms). The presence of an inversion in the opposite chromosome suppresses the clastogenic effect of the deletion. This effect is presumed to be due to the formation of the conjugational loop in the region of pericentric heterochromatin which subsequently breaks.

Animals↗