To adjust breeding programs for local, commercial, and fancy breeds, and to implement molecular (marker-assisted) breeding, a proper comprehension of phenotypic and genotypic variation is a sine qua non for breeding progress in animal production. Here, we investigated an evolutionary subdivision of domestic chickens based on their phenotypic and genotypic variability using a wide sample of 49 different breeds/populations. These represent a significant proportion of the global chicken gene pool and all major purposes of breed use (according to their traditional classification model), with many of them being characterized by a synthetic genetic structure and notable admixture. We assessed their phenotypic variability in terms of body weight, body measurements, and egg production. From this, we proposed a phenotypic clustering model (PCM) including six evolutionary lineages of breed formation: egg-type, meat-type, dual purpose (egg-meat and meat-egg), game, fancy, and Bantam. Estimation of genotypic variability was carried out using the analysis of five SNPs, i.e., at the level of genomic variation at the NCAPG-LCORL locus. Based on these data, two generally similar genotypic clustering models (GCM1 and GCM2) were inferred that also had several overlaps with PCM. Further research for SNPs associated with economically important traits can be instrumental in marker-assisted breeding programs.

The color of plumage in birds is an important feature, often determining descent to a particular species or breed. It serves as a key factor in the interaction of birds with each other due to their well-developed visual perception of the surrounding world. In poultry including chickens, the color of the plumage can be treated as a genetic marker, useful for identifying breeds, populations and breeding groups with their specific traits. The origin of diverse color plumage is the result of two interrelated physical processes, chemical and optical, due to which pigment and structural colors in the color are formed. The pigment melanin, which is presented in two forms, eumelanin and pheomelanin, is widely spread in birds. The basis for the formation of melanin is the aromatic amino acid tyrosine. The process of melano-genesis involves many loci, part of the complex expression of plumage color genes. In birds, the solid black color locus encodes the melanocortin 1 receptor (MC1R), mutations in which lead to a change in receptor activation and form different variants of the E locus. Using the GWAS analysis, possible genes affecting the formation of color in chickens were detected. The biosynthesis and types of melanin are affected by the activity of the enzyme tyrosine, and mutations in the tyrosinase gene (TYR) cause albinism in different species. The formation mechanism of brown, silver, gold, lavender and a number of other shades is determined by the influence on the work of the MC1R genes and TYR specific modifier genes. Thus, locus I currently associated with the PMEL17 gene inhibits the expression of eumelanin, and the MLPH gene affects tyrosinase function. Research on the mechanisms of formation of the secondary coloring of plumage in chickens is being actively conducted nowadays. The formation of a marble feather pattern is associated with the mutation of the endothelin B2 receptor (EDNRB2), in the coding part of the gene of which a polymorphism is found associated with the mo locus. The molecular base that causes the feather banding (locus B and autosomal recessive banding) is identified. Today, only some genes that determine the color of the plumage of chickens are studied and described. Different genes can produce similar plumage patterns, and different phenotypes can be determined by the polymorphism of a single gene. Using molecular methods, you can more accurately identify these differences. This overview shows the nature of melanin coloration in birds using the example of chickens of various breeds and also attempts to systematize knowledge about the molecular-genetic mechanisms of the appearance of various types of coloration.

Monitoring the genetic diversity of small populations is important with respect to conserving rare and valuable chicken breeds, as well as discovery and innovation in germplasm research and application. Restriction fragment length polymorphisms (RFLPs), the molecular markers that underlie multilocus DNA fingerprinting (MLDF), have historically been employed for this purpose, but over the past two decades, there has been an irreversible shift toward high-throughput single-nucleotide polymorphisms (SNPs). In this study, we conducted a comparative analysis of archived MLDF results and new data from whole-genome SNP genotyping (SNPg) among 18 divergently selected breeds representing a large sample of the world gene pool. As a result, we obtained data that fit the general concept of the phylogenetic distribution of the studied breeds and compared them with RFLP and SNP markers. RFLPs were found to be useful markers for retrospective assessment of changes in the genetic architecture and variability underlying the phenotypic variation in chicken populations, especially when samples from previous generations used for MLDF are unavailable for SNPg. These results can facilitate further research necessary to assess the possibility of extrapolating previous MLDF results to study the long-term dynamics of genetic diversity in various small chicken germplasm populations over time. In general, the whole-genome characterization of populations and breeds by multiple SNP loci will further form the basis for the development and implementation of genomic selection with the aim of effective use of the genetic potential of the domestic gene pool in the poultry industry.

In the poultry industry, indicators reflecting the growth rate of young stock and the exterior characteristics of chickens are important benchmarks for breeding. Traditional selection based on phenotypic evaluation is characterized by low efficiency with a low character inheritance ratio and is difficult to apply in small groups of animals and birds bred in bioresource collections. The use of molecular genetic markers associated with economically important traits makes it possible to carry out early selection of birds. This entails an increase in the profitability of the poultry industry. Recently, single nucleotide polymorphisms (SNPs) have served as convenient markers for selection purposes. For five generations (P1–P5), an experimental selection of hens of the Pushkin breed was carried out for live weight. It was based on selection for single nucleotide polymorphism rs313744840 in the MSTN gene. As a result, a significant increase in the frequency of allele A in this gene, from 0.11 to 0.50, took place. The association of SNP markers with meat qualities in the experimental group led to changes in the exterior profile of an adult bird at 330 days of age. The individuals with the AA and AG genotypes had the greatest live weight and longest body. As a result of selection, the bird on average became larger due to an increase in the number of heterozygous individuals with long bodies and large chest girths. The depth of the chest and the width of the pelvis increased due to an increase in the frequency of allele A in the experimental population. A tendency towards an increase in these indicators with the substitution of G with A in the genotype was found. Saturation of the population with desirable alleles led to an increase in the average live weight of the chickens. Analysis of the exterior parameters of adult birds showed that this growth is achieved by increasing the depth and volume of the bird body, and not by increasing the length of the limbs. Thus, marker selection carried out for five generations in the experimental population of Pushkin breed chickens to increase body weight has reliably (p < 0.001) changed the exterior profile of adult birds.

   Relevance. The demand for organic meat products is constantly increasing. Organic agriculture is the leading global trend. The organic market for 2020 is estimated at $ 130 billion with an annual growth of 13–15 %. During the pandemic, sales of organic products in developed countries increased by 30–40 %.   Methods. The object of the study were chickens of the Pushkin breed and the Ross 308 cross (broiler). The birds were grown up to 85 days of age under the same conditions, the stocking density was 10 birds/m². At the age of slaughter in industrial production (48 days – broiler) and organic production (85 days) according to the methodology of the All-Russian Research and Technological Institute of Poultry (2001), anatomical cutting of 9 heads was carried out. Analysis of quality indicators of meat by high performance liquid chromatography (M02-902-142-07) was carried out in the certified laboratory «Leningradskaya MVL». Dry matter was determined by the express method according to the Rygalova E. A. and the water binding capacity of meat was determined by the Grau – Hamm method in the Volovinskaya – Kelman modification.   Results. Extending the fattening period of broilers to 85 days to meet the requirements of organic poultry farming does not sufficiently improve the quality of their meat. Low livestock safety (58.16 %) reduces the profitability of organic broiler production. An increase in the total protein content from 20.44 % to 24.41 % and amino acids (tryptophan and prolin), as well as a decrease in fat content from 5.1% to 1.35 % in the pec-toral muscle of broiler chickens from 45th to 85th day improves the dietary qualities of broiler meat. However, a decrease from 51.46 % to 48.54 % of the water-binding capacity of meat reduces its taste and techno-logical qualities. In chicken of the Pushkin breed this figure is 51.35 %. Thus, using the example of the Pushkin breed of chickens, it is shown that breeds of the combined direction of productivity are more suitable for long-term cultivation in organic poultry farming for obtaining meat products.

In meat-type poultry breeding, pectoral angle (PA) is a conventional anatomical indicator for changes in body conformation and meat traits; its correlation to egg performance is however deemed controversial. In this context, we revisited, assessed and put forward evidence for the usefulness of this classic phenotypic variable and its specific integrative index of pectoral angle-to-body weight ratio (PA/BW). Specifically, we identified respective correlations and used them for distinguishing the major categories (production types) of diverse chicken breeds under the traditional classification model (TCM) and genotypic clustering models of the global chicken gene pool subdivision. Also, the usefulness of the supplementary integrative egg mass yield index (EMY) for this objective was demonstrated. Because of estimating the total mass of eggs laid (i.e. egg number times egg weight), EMY can serve as an indicator of egg production. Direct approximation of EMY values by PA and BW values did not lead to significant correlation dependences between these indicators in each of the four breed utility types according to TCM. However, using the ratio of PA to BW, instead of PA and BW alone, resulted in significant correlation of EMY with PA/BW, allowing for distinction between egg-type and non-productive breeds. The validity of the proposed correlation-based models was supported by PCA and Neighbor Joining clustering analyses. Collectively, we suggested that PA can be a potentially correlated trait for selecting hens and roosters in breeding flocks to boost egg yield. These results can also be applied to chicken breeding as well as conservation- and phenome-related research.