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Kompleksy synaptonemalne

100%

Czyżewska D. , Andraszek K. , Smalec E.

tom 56

nr 3-4

349-359

Genetic recombination is the main cause of changeability of different organisms. Synaptonemal complex (SC) is a protein structure which controls correct course of coniugation and the frequency of crossing over. It binds chromosomes into the biwalents. This structure consists of central element (CE) and two lateral elements (LE) related to the chromatin. There are observed ovale structures between lateral elements called recombination nodules (RNs). Recombination nodules are multienzimatic complexes, which catalize DSBs (Doubble Strand Breakes) and crossing over process. Synaptonemal complex is very important in meiosis pairing, but there are several taksons which do not form this structure, for example D. melanogaster male. Interesting modifications of synaptonemal comlexes are observed in heterohromosomes, which show slight homology, like the ZW pair in birds or some insects. A few organizms, such as eutherian mammals, form Danse Plate between heterochromosomes instead SC. There is observed interlocking during pairing sometimes, when chromosome or bivalent stuck between another pair of homologs. There are also observed in many organisms policomlexes consisting of synaptonemal's complex elements. In most events immunostaining metods are used to test function and structure of synaptonemal's complex elements.

Rola sekwencji (TTAGGG)n w badaniach kariotypu i ewolucji ptaków

100%

Andraszek K. , Wójcik E. , Smalec E. , Gągała U.

tom 57

nr 1-2

109-118

As in mammalian chromosomes, avian chromosomes consist of 5'-(TTAGGG)n-3'repeats, the sequence being the pattern conserved throughout vertebrate evolution. Although the avian genome is only 1/3 of the average mammalian genome, the telomeric sequences constitute as much as 4% of it and occur ten times more often than in mammals. What is particularly interesting from the point of view of bird karyotype evolution is research on the localization of telomeric sequences in the interstitial parts of chromosomal arms. Interstitial telomeric sequences occur on macro- and microchromosomes, and their distribution, especially of those located on macrochromosomes, varies a lot. Interstitial telomeric sequences act as hot recombination places and they are correlated with occurrence of chiasms. High frequency of telomeric sequences in bird microchromosomes also results in a particularly high rate of microchromosome recombination. Determination whether interstitial telomeric sequences on macrochromosomes are evolutionary places of microchromosomal fusions is a very significant issue in studies on bird telomeric sequences.

Telomery - duża rola małych sekwencji

100%

Gągała U. , Andraszek K. , Wójcik E. , Smalec E.

tom 57

nr 3-4

331-341

Telomeres are distal structures of eukaryotic chromosomes, which are responsible for their stability and functioning. They assure complete replication of terminal fragments of chromosomes, prevent degradation and fusion of chromosomes. Telomeres of most chordates are comprised of tandem repeats of the basic unit 5'-(TTAGGG)n-3'. The number of repeats of the basic telomeric sequence differs between the chromosomes of one and the same cell. However, in remains within the strictly determined range for a given species, for man it ranges from 2 to 30 th pairs of nucleotides. Younger cells have got longer telomeres whereas the telomeres of older cells are shorter. Cytogenetic studies on telomeric regions of chromosomes have gained significance since the moment of the discovery that this chromosomal fragment actively participates in the process of cancer development, cell ageing and apoptosis. Telomeres consist of non-coding DNA sequences. They contain no genes and they code no proteins but their role in medicine, genetics and evolutionary studies is becoming more and more significant.