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In this study an attempt was made to analyse morphological changes in sperm with particular attention to sperm with a cytoplasmic droplet, taking into account the age and breed of the boar. The material for the study consisted of ejaculates of insemination boars of five breeds. Morphological examination of sperm was carried out in 30 randomly selected boars--6 individuals from each breed. The morphology of 500 spermatozoa was evaluated in each slide. The percentage of sperm with normal morphology in the semen of the boars varied between breeds and was dependent in varying degrees on the age of the boar. The primary defects in sperm occurred more frequently in Duroc and Pietrain boars than in other breeds and were more dependent on the age of the boar. The high percentage of primary defects in the sperm of young Duroc boars was determined by the frequency of sperm cells with a proximal cytoplasmic droplet on the midpiece. A particularly high percentage of sperm cells with secondary defects was noted in the initial stage of the reproductive life of the boars. The high number of sperm cells with secondary defects noted in the semen of the Duroc and Pietrain boars and the changes occurring with age in the frequency of secondary morphological defects were mainly determined by the frequency of sperm cells with a distal protoplasmic droplet in the middle piece and to a lesser degree by that of sperm cells with a pseudodroplet.

Nucleoli are the product of the activity of nucleolar organizer regions (NOR) in certain chromosomes. Their main functions are the formation of ribosomal subunits from ribosomal protein molecules and the transcription of genes encoding rRNA. The aim of the study was to determine the shape of nucleoli and analyse methylation in the gene RN28S in the spermatocytes of male Japanese quail (Coturnixjaponica) in two age groups. Nucleoli were analysed in cells of the first meiotic prophase. Their number and shape were determined and they were classified as regular, irregular or defragmented. In the cells of the young birds no defragmented nucleoli were observed, with regular and irregular nucleoli accounting for 97% and 3%, respectively. In the cells of older birds no regular nucleoli were observed, while irregular and defragmented nucleoli accounted for 37% and 67%, respectively. MSP (methylation-specific PCR) showed that the gene RN28S is methylated in both 15-week-old and 52-week-old quails. In recent years an association has been established between nucleolus morphology and cellular ageing processes.

DNA methylation is an epigenetic modification that plays an important role in the proper development and functioning of an organism. The DNA methylation level is species-, tissue- and organelle-specific, and the methylation pattern is determined during embryogenesis. A correlation between methylation and age is also observed. Epigenetic phenomena are an enormously interesting research subject, not only from the perspective of pure science, but also due to their possible applications in medicine. The aim of this study was to determine the global DNA methylation level in relation to the developmental stage of the embryo. The global level of 5-methylcytosine in the DNA during pulmonary respiration was found to be higher than during allantoic respiration. The analysis shows a clear dependence between the stage of individual development and the global DNA level of 5-methylcytosine. In the future, methylation level may be a determinant of age and perhaps even a tool for predicting life expectancy. Abnormalities in the methylation process result in premature ageing at the cellular and individual level.

Methylation is an epigenetic modification of DNA affecting gene expression without changing the structure of nucleotides. It plays a crucial role in the embryonic and post-embryonic development of living organisms. Methylation level is tissue and species-specific and changes with age. The study was aimed at identifying the methylation of the CDKN2B gene situated at locus bar in Polbar chickens on the 6th and 18th day of embryonic development using the MSP (methylation-specific PCR) method. Methylation was not detected in the promoter region of gene CDKN2B on the 6th and 18th day of embryonic development. As one of the five genes responsible for melanine activity in melanocytes and highly active, it can contribute to the production of this pigment. The present research broadens the current knowledge of the chicken epigenome and the mechanism of autosexing in birds.

Nucleoli are the product of nucleolus organizing region activity (NOR) of specific chromosomes. Their basic function is to synthetise ribosomal RNA precursors and promote the maturation and assemblage of preribosomal RNP molecules. Information on rRNA-coding gene activity can be provided by the analysis of the number and size of nucleoli in the prophase of the first meiotic division. The morphology and ultrastructure of a nucleolus depends, among others, on the species and cell growth cycle as well as the physiological and pathological state of an organism. The purpose of this research was to determine the number and size of nucleoli in the spermatocytes of the domestic chicken and the Japanese quail. Diverse numbers and sizes of nucleoli in the cells of the analysed birds were observed. 1-4 nucleoli were identified in chicken cells (1.91 +/- 0.63 on average) and 1-2 in quail cells (1.13 +/- 0.33 on average). For the total of 957 nucleoli observed in Gallus cells, 329 were classified as large and 628 as small. In Coturnix cells, 563 nucleoli were identified (66 large and 497 small ones). An analysis of the numbers and sizes of nucleoli can be performed at the cytogenetic level and serve as an alternative source of information on rRNA encoding gene and nucleolus organising region (NOR) activities.

Lampbrush chromosomes (LBCs) present in bird oocytes are a new model in cytogenetics with particular significance for bird chromosome analysis. The fact that female birds are heterogametic makes it possible to observe both sex chromosomes in the form of decondensed structures typical of lampbrush chromosomes. A change in transcription activity associated with physiological processes in geese prior to and after the reproductive season is reflected in chromosome morphology. Lampbrush chromosomes obtained after the reproductive period have reduced side loops, sites of intensive transcriptional activity. However, noticeable characteristics in the chromosomes include inactive chromomeres. Chiasms, PBs, large side loops (ML) and telomeric loops (T, TLL, and GLL) are structures that undergo degradation latest after the termination of reproduction, and as a result, constitute the basis of identification of individual bivalents in different periods of the cell's transcriptional activity.

The synaptonemal complex (SC) is a protein structure which binds two homologues during prophase of the first meiotic division and assures the correct course of genetic recombination. The demonstration and identification of SCs in European domestic goose Anser anser was the aim of the current research. Standard techniques of SC identification do not allow for an analysis of their molecular structure. In meiotic cells of one-day-old nestlings and 17-week-old geese the haploid number of bivalents, darkly stained kinetochores and subtelomeric regions may be evidence for the presence of SCs. Experimental chromosome staining with the DAPI fluorochrome permitted the observation of the characteristic ladder-like structure of SCs and the course of synapsis formation within homologues from early leptotene to their degradation in late pachytene. The detailed molecular structure of synaptonemal complexes can be analysed with an electron or scanning microscope only. Because the bivalent is a direct result of the complex's presence, in the literature the presence of bivalents is equivalent to the term "synaptonemal complex". However, the bivalent and the SC are two different structures.