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Epigenetic mechanisms, such as DNA methylation, RNA interference, posttranslational histone modifications and rearrangements of chromatin structure play an important role during genome reprogramming in both animals and plants. The correct epigenetic pattern of eu- and heterochromatin marks allows for maintaining chromatin in an active or transcriptionally silenced state. In the life cycle of angiosperms, epigenetic mechanisms participate in genome reprogramming during: 1) differentiation of sporophyte cells into spore mother cells (SMC) that undergo meiosis, 2) development of female and male gametophytes, within which the gametes differentiate and 3) after double fertilization during the embryo and endosperm development. SMC speciation and control of meiosis, followed by reprogramming of the sperm cells and egg cell genome, are non-cell-autonomous and require RdDM pathway. These processes involve companion cells, which produce „mobile” siRNAs signal molecules. Epigenetic control of gene expression through siRNAs also participates in maintenance of gametes and embryo genome integrity and in the parental imprinting.

The article presents three standpoints on the question of moral permissibility of human cloning and shows the philosophical principles of it. 1. The moral consent to human cloning with the purposes of reproduction and therapy. The followers of human cloning refer to materialistic anthropology also to subjectivistic, relativistic and utilitarian ethics. 2. Those, who are adverse to human cloning with the purpose of reproduction, but they acquiesce to the so-called therapeutic cloning. They reject that human embryos and foetuses are individuals who come under protection of law. 3. Those, who reject human cloning for the purposes of reproduction and therapy alike. They assent to a personalistic anthropology and Christian ethics. A human being was created by God and human life begins at the moment of insemination. All three groups use various argumentation. The arguments for and against cloning are extracted from biology as well as psychology, philosophy, law and religion. The author of the article takes the last standpoint, but she does not see such arguments, that might convince the opposite parties to a suit.

The more we know, the more duties and greater responsibility we have. The dynamic development of biology carries a lot of hope for the freeing of mankind from genetic diseases. But the introduction of scientific thought necessarily has to be bound with the development of technology. It is wrong when technology dictates science a direction of development; when technique comes before ethics; and when technology does not respect the essence of a human being. The uncritical introduction of eugenics, especially cloning of people and rejecting all moral arguments, recalls inglorious acts of science when the ideology of progress determined the range of problems that researchers focused on. The same ideology of progress, although originating from other sources, pushes science toward a second extreme, into utilitarianism. In the article the author wishes to substantiate the necessity for researchers to respect ethical norms. Recognition of natural laws alone does not provide science with full development if the rights of conscience are violated.

One does not see a possibility for moral justification of the cloning of humans, or of any other experiments and manipulation of human embryos other than on the grounds of materialistic anthropology which reduces human spirituality to the dimensions dealt with by natural sciences. If, however, man is a person, and if "to be a person" constitutes an ontological situation and is not the result of some kind of social contract, and if the human embryo is, at least potentially a person, then the Kantian personalistic norm will demand a ban on the cloning of humans and on experimenting on human embryos, and will also exclude any attitude of ownership towards each human being. This demand seems all the more clear if we look at the personalistic norm from the point of view of what is most wonderful in being a person namely, that the person is capable of receiving, learning and giving love. The deficiency of love received at the beginning of somebody's life - even if he or she was conceived out of love - may be a cause of this person becoming closed to higher values. Thus, the idea of cloning human beings means to structurally remove love from the beginning of human life and to introduce technology instead. One cannot really do more harm to another person than by depriving him or her of love at the very beginning of his or her life. I think that the well known stories about Golem or Frankenstein express a presentation of just this truth - and that is why they are so terrifying.

Most of the human chromosomal abnormalities seems to be of a germ-cell origin. Human oocytes are difficult to obtain and to handle, so most of the studies has been performed on male gametes. Genetic status of spermatozoa may be critical for human reproduction as well as wellbeing of fetus. The ability to identify and to characterize chromosomal aberrations in human sperm would lead to understanding of the mechanism causing chromosomal abnormalities and to approach possible preventive strategies. The aim of this paper was to present current data concerning the chromosomal aberations in human spermatozoa. Presented overview strongly underlines the importance of genetic investigations of male gametes.