Heterochromatin variants of the human karyotype

Chromosomes are cell structures consist of chromatin, out of which one kind is a constitutive heterochromatin, which contains non-coding sequences only and is transcriptionally inactive. Heterochromatin blocks consist of highly repetitive sequences of satellite DNAs, which allows the parts to be variable. The largest areas of heterochromatin can be found at long arms of chromosomes 1, 9, 16 and Y, but heterochromatin areas also affect the variability of the short arms of acrocentric chromosomes 13 - 15, 21 and 22. This bachelor thesis based on a number of scientific essays summarizes findings about heterochromatic variants, their occurrence, frequency, possibilities of examining as well as their clinical significance in today's world. It mainly highlights their possible connection with reproductive failures and contradictory results of individual observations. Contemporary results show the importance of new laboratory methods (molecularly cytogenetic), which can be used in specifying and more detailed sorting of findings, which were previously tagged as harmless variants according to less accurate banding methods. The summarization implies that emphasis should be put on the study of clinical meaning of heterochromatic variations. These can influence the progress of meiosis and thus trigger..