continually improved cytogenetic techniques (differential staining and high resolution banding techniques), complemented with the molecular genetics methods (fish and prins), enable chromosomal mutations to be accurately identified in the karyotype of the pig (Sus scrofa). the major breeding problem are balanced mutations because of their hidden nature, as they affect the animals with normal body conformation (and normal semen parameters in boars), which transfer these aberrations to the next generations and disseminate in the population. this refers to the structural rearrangements (translocations and inversions), causing developmental abnormalities and considerably reducing fertility and productivity parameters in breeding herds, which results in substantial financial losses. Routine karyotype screening using modern cytomolecular diagnostic methods is necessary due to the potential emergence of new mutations and the rapid spread of these genetic defects in the population, especially under artificial insemination conditions.

Gene expression analysis by Real-Time PCR requires careful selection of endogenous reference genes to obtain accurate results. We evaluated usefulness of six reference genes to expression studies of porcine stomach. We selected genes which were recently described as very stable (RPL27, RPS29, RPS13, OAZ1) and two commonly used housekeeping genes (GAPDH, ACTB). Our results indicate that OAZ1, RPS29 and RPL27 are more suitable reference genes than ACTB and GAPDH in expression studies of porcine stomach. In our study the most stable genes were OAZ1 (M=0.856), RPS29 (M=0.862) and RPL27 (M=0.892), while ACTB (M=1.03) and GAPDH (M=1.005) were less stable. RPS13 (M=1.913) appeared to be highly unstable.Set of three the most stable genes has been used to compare ghrelin (GHRL) expression in two different regions (diverticulum ventriculi and fundus ventriculi) of porcine stomach. Ghrelin mRNA was highly expressed in both regions of stomach, however level of GHRL mRNA was approximately 5-fold higher in fundus ventriculi than in diverticulum ventriculi.

The Drosophila-like homolog 1 (DLK1), a transmembrane signal protein similar to other members of the Notch/Delta/Serrate family, regulates the differentiation process in many types of mammalian cells. Callipyge sheep and DLK1 knockout mice are excellent examples of a fundamental role of the gene encoding DLK1 in muscle growth and fat deposition. DLK1 is located within co-regulated imprinted clusters (the DLK1/DIO3 domain), along with other imprinted genes. Some of these, e.g. the RNA coding MEG3 gene, presumedly interfere with DLK1 transcription. The aim of our study was to analyze DLK1 and MEG3 gene expression in porcine tissues (muscle, liver, kidney, heart, brain stem) during postnatal development. The highest expression of both DLK1 and MEG3 variant 1 (MEG3 var.1) was observed in the brain-stem and muscles, whereas that of MEG3 variant 2 (MEG3var.2) was the most abundant in muscles and the heart. During development (between 60 and 210 days of age) expression of analyzed genes was down-regulated in all the tissues. An exception was the brain- stem, where there was no significant change in MEG3 (both variants) mRNA level, and relatively little decline (2-fold) in that of DLK1 transcription. This may indicate a distinct function of the DLK1 gene in the brain-stem, when compared with other tissues.

IGF2 is one of the genes that control muscle development. Moreover, IGF2 is imprinted, as only the paternal allele is expressed in the offspring. Using real-time PCR for IGF2 genotyping (Carrodegous et al. 2005), we evaluated the frequency of the IGF2 A3072G mutation (Van Laere et al. 2003) in pigs: Polish Landrace (PL, N = 271) and Large White (LW, N = 267). Our results are consistent with previous reports, showing that the A allele is common in breeds subjected to strong selection for lean meat content (A allele frequency was 0.79 in LW and 0.69 in PL). Moreover, we compared body composition, growth performance and meat quality traits in pigs carrying opposite genotypes (A/A and G/G) in the IGF2 gene. The association study revealed that the A allele increases the weight of loin (WL) (additive gene effect = 450 +/- 50 g in LW and 213 +/- 64 g in PL), weight of ham (WH) (544 +/- 48 g in LW and 302 +/- 72 g in PL), loin eye area (LEA) (4.9 +/- 0.46 cm(2) in LW and 2.1 +/- 0.95 cm(2) in PL), carcass meat percentage (CP) (3.12 +/- 0.27% in LW and 1.89 +/- 0.47% in PL), and decreases average backfat thickness (ABF) (-0.2 +/- 0.036 cm in LW and -0.2 +/- 0.048 cm in PL). Additionally, in PL, the A allele increases the weight of tenderloin (WT) (11 +/- 0.01 g), average daily gain (ADG) (30.7 +/- 17.29 g), and decreases feed intake (F) (-121 +/- 45 g) and days of feeding (DF) (-3.5 +/- 2.08 days). No significant effects were observed for meat quality traits. Our results suggest that selection based on the IGF2 mutation in Poland may be very useful in PL and LW pigs, where the G allele is still relatively frequent.

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