Viable Translocations Research Articles

Time-lapse imaging reveals delayed development of embryos carrying unbalanced chromosomal translocations.

The purpose of the study was to compare the morphokinetic parameters of embryos carrying balanced chromosomal translocations with those carrying unbalanced chromosomal translocations using time-lapse microscopy. The study group included 270 embryos that underwent biopsies on day 3 for preimplantation genetic diagnosis (PGD) for chromosomal translocations in our unit between 2013 and 2015. All embryos were incubated under time-lapse microscopy and evaluated for timing of developmental events up to day 5. The timing of these events was compared between balanced and unbalanced embryos, potentially viable and nonviable variants, and maternal versus paternal inheritance of the translocation. The PGD analysis found that 209 (77%) of the 270 biopsied embryos carried an unbalanced translocation. Embryos carrying unbalanced translocations, which are expected to lead to implantation failure or miscarriage, cleaved less synchronously and were delayed in time of cleavage to the 4-cell stage (t4) and in time of start of blastulation (tSB) compared with balanced embryos (P < 0.05). Furthermore, embryos carrying nonviable translocations demonstrated a significant delay at the time of pronuclei fading (tPNf) compared with those carrying potentially viable translocations (P < 0.05). Embryos whose unbalanced translocations were of maternal origin were significantly delayed in most of the morphokinetic parameters (including tPNf, t2, t3, t4, t6, t7, t8, cc2, s2, and tSB) compared with embryos carrying balanced translocations (P < 0.05). Embryos carrying unbalanced chromosomal translocations mainly of maternal origin undergo delayed development and asynchronous cleavage that may lead to implantation failure or miscarriage.

Gamma-rays induced reciprocal translocation inNigella damascenaL. (Love-in-a-mist)

AbstractGamma irradiations (5, 10, 15 and 20 kR) to Nigella damascena L. (love-in-a-mist; family: Ranunculaceae) seeds (moisture content: 8.7%) induced three viable translocation heterozygotes (P-3 and P-15 from 5 kR and P-25 from 10 kR) which on selfing yielded progeny heterozygotes in subsequent generations (R2, R3 and R4; however, P-15 could only be assessed upto R2 generation) exhibiting the formation of either a ring or a chain of four chromosomes in 14.8–54.6% meiocytes. Mean quadrivalent frequency per cell was assessed to be 0.40–0.66 in P-3, 0.43–0.64 in P-15 and 0.15–0.47 in P-25. Configuration and orientation of the multiples in the heterozygotes assessed over the generations indicated a possible genetic control over the mechanism. Normal 6/6 separation of chromosomes at AI (55.86–100.00%) of the heterozygotes did not correlate significantly (r = 0.29,27 DF) with pollen fertility (6.98–46.38%). Pollen fertility showed negative and insignificant correlation (r = -0.20,27 DF) with seed set per pla...

Gamma-rays Induced Reciprocal Translocation in Black Cumin(Nigella sativa L.).

Gamma irradiations (5, 10, 20 kR) to Nigella sativa L. (black cumin) seeds (moisture content 7.5%) induced 5 translocation heterozygotes (P-14 and P-26 from 5 kR and P-32, P-36 and P-37 from 10 kR). P-14, P-32 and P-36 were viable translocations; while, P-26 and P-37 yielded only abortive seeds at R1 following selfing and on open or controlled pollination. The translocation heterozygotes exhibited the formation of either a ring or a chain of 4 chromosomes in 38.71% to 77.72% meiocytes. Predominance of rings occurred in all translocation heterozygotes excepting P-26 where rings and chains were nearly equal. P-14 and P-26 had more adjacent orientation of quadrivalents than alternate; while, P-32, P-36 and P-37 demonstrated random orientations. The quadrivalent behaviour was found to be persistent in all generations of P-14, P-32 and P-36. The rings showed preponderance of adjacent orientation and the chains demonstrated frequent alternate orientation. Though normal 6/6 separation of chromosomes at AI was observed in 85.8, 83.3, 69.4, 82.3 and 86.4% cells of P-14, P-26, P-32, P-36 and P-37 respectively, pollen fertility was reduced in the heterozygotes (8.2 to 37.5%). F1’s raised from intercrossing of P-14, P-32 and P-36 were meiotically assessed and the results indicated that same 2 non-homologous chromosomes were involved in translocation and the 2 longest chromosome pairs AA and BB (nucleolar pair) were suggested to be associated. P-14, P-32 and P-36 had marker phenotypic traits and characteristically P-36 possessed non-shattering capsule trait.

Different chromosomal distribution patterns of radiation-induced interchange breakpoints in barley: First post-treatment mitosis versus viable offspring

Translocation breakpoints (TBs) induced by ionizing radiation are nonrandomly distributed along barley chromosomes. When first post-treatment mitoses were evaluated, centromeres and the heterochromatin-containing proximal segments tended to be more than randomly involved, and terminal segments to be less than randomly involved in translocations. Contrary to this, small chromosomal regions in median and distal arm positions, characterized by high recombination rates and high gene density, were identified as preferred sites for the origination of viable translocations, probably due to deviations in chromatin organization. Apparently, the position of a TB has an influence on the rate of viability versus elimination of the carrier cells. Surprisingly, TBs within centromeres and heterochromatin-containing segments seem to be more harmful for survival than those induced in gene-rich regions.Key words: Hordeum vulgare, radiation-induced chromosome breaks, translocation lines, breakpoint distribution.

Different chromosomal distribution patterns of radiation-induced interchange breakpoints in barley: first post-treatment mitosis versus viable offspring.

Translocation breakpoints (TBs) induced by ionizing radiation are nonrandomly distributed along barley chromosomes. When first post-treatment mitoses were evaluated, centromeres and the heterochromatin-containing proximal segments tended to be more than randomly involved, and terminal segments to be less than randomly involved in translocations. Contrary to this, small chromosomal regions in median and distal arm positions, characterized by high recombination rates and high gene density, were identified as preferred sites for the origination of viable translocations, probably due to deviations in chromatin organization. Apparently, the position of a TB has an influence on the rate of viability versus elimination of the carrier cells. Surprisingly, TBs within centromeres and heterochromatin-containing segments seem to be more harmful for survival than those induced in gene-rich regions.

Analysis of the Functional Significance of Linkage Group Conservation in Drosophila

Linkage groups, as defined by chromosome arms in Drosophila melanogaster, appear to have remained largely intact within the genus Drosophila and, possibly, within the higher Diptera per se. We hypothesized that linkage group conservation might have a functional basis (possibly related to interphase chromosome arrangement). To test this hypothesis, a series of autosomal 2-3 translocations were synthesized, creating many new linkage groups. A total of 167 2-3 translocations were recovered, cytologically analyzed to determine their polytene chromosome breakpoints, and tested for homozygous viability and fertility. The breakpoints associated with homozygous viable translocations were randomly distributed throughout the genome, indicating that the linear continuity of the linkage groups could be disrupted quite extensively. Inter se complementation crosses between homozygous lethal translocations having similar breakpoints further confirmed this result, documenting that, at least with respect to homozygous viability, the linear integrity of the autosomal linkage groups was not of major functional significance. Fertility analysis of the homozygous translocations also indicated that sterility could not be a single major factor. Having concluded that linkage group conservation is not based on important functional interactions between specific linked chromosomal segments, or due principally to the sterility of new linkages, the problem of linkage group conservation remains unsolved. Several possible selective factors are discussed, principally segregational load and inbreeding depression, which may contribute to the elimination of new linkage rearrangements.

Possible use of translocations to fix desirable genes in insect pest populations.

CHROMOSOME translocation heterozygotes (T/+) are usually semisterile, but translocation homozygotes (T/T) if viable are usually fully fertile. If such a viable translocation were produced in an insect pest, T/T insects could be reared in captivity and released into the wild, where matings with wild types (+/+) would produce T/+ progeny.

Radiation-induced chromosomal aberrations and lethals in Aspergillus nidulans.

The frequency of translocations induced in diploid conidia of Aspergillus nidulans by gamma rays was much higher than that of recessive mutants involving a single chromosome. More than half of the surviving nuclei contained viable translocations at radiation doses within the range normally employed for induction of mutants in microorganisms.