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This presentation has been supported by the Erasmus+ KA2   
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Cooperation Partnerships grant no. 2021-1-SK01-KA220-HED-000032068 

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“Innovation of the structure and content of study programs in the field of animal genetic and food resources management with the use of digitalisation

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The European Commission support for the production of this presentation does not

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constitute an endorsement of the contents which reflects the views only

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of the authors, and the Commission cannot be held 

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responsible for any use which may 

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be made of the information contained therein

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This presentation

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has been created

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 by Stanislav Socha
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professor at

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Siedlce	

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University

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Institute of Zootechnic and Fisheries.

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The topic will be concerning
sources of variation in the population,

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as well as genetic and environmental variability.

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Phenotype, genotype 

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and environment

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The value of the phenotype

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depends on the genotypic value of the individual

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influence of environmental conditions.

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Characteristics important in animal husbandry include traits

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related to the performance of animals, e.g.

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milk yield, animal reproduction and health.

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Generally, the features can be classified into two groups

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quality features and quantitative characteristics of

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group, etc..

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Quantitative features and qualitative features

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The main factor

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differentiating these two groups of features
is the number of pairs of alleles

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also called genes affecting their shape and the number

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of classes of differentiated phenotypes.

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In the case of qualitative traits,

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the number of pairs of genes or a series of alleles

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influencing their formation is limited and varies

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within quite narrow limits from 1 to a maximum of 2 to 4.

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This, in turn affects a limited number of genotypes.

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Hereditary assumptions of individuals
and as a result individuals with specific phenotypes.

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All the characteristics of the organism.

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for examples

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of quality characteristics include

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animal color, row, feather color in poultry,

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horned or polled cattle, sheep and goats.

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Blood groups systems. 

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In the case of features defined as quantitative.

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The situation is much more complex.

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Firstly, the number of genes polygons

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affecting their shape is very numerous,
sometimes difficult to determine.

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Then, in addition to genetic assumptions,

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environmental factors
have a significant impact on their formation.

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This type of inheritance not only significantly increases
the diversity of individuals in the herd,

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but also makes it extremely difficult to identify genotypes

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based on phenotype.

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HERITABILITY OF TRAITS

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With the multiplicity of factors affecting traits.

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It is impossible to determine the contribution of a single gene
to the formation of a quantitative trait.

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Only statistical methods
allow to determine the influence of genotype

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and environment
on the variability of the trade in the herd population.

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And to estimate the heritability

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of the traits of interest on this basis.

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It is the variation in the value

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or quality of traits observed among individuals in a herd.

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In a population.

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Genetic
variation is the basis for the genetic improvement of animals.

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Its sources are.

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Recombination leads to the formation of different new genotypes,

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and mutations lead to the formation of new genes.

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Other systems within a chromosome or between chromosomes.

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According to Jeżewska-Witkowska , 2010.

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The three main reasons for variability are aesthetic-

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diversity of forms in nature, material nature-

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A variety of products is necessary
to meet your needs and improvement-

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Thanks to the variability
the breeder can select the best animals

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for a given trait for further breeding.

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In animal husbandry,
knowledge of genetics can prove quite useful,

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as it can help with improvement of animals, production
planning for market needs.

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For example, coat color marking color of subcutaneous fat.

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Color of shell in animal reproduction,

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predicting their vitality, temperament and physique.

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The possibility of avoiding defects
and diseases of genetic origin,

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creating lines of laboratory animals
for the needs 

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of human 

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medicine

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Variability of quantitative features and selection difference

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RELATIONSHIP BETWEEN AN INDIVIDUAL'S PHENOTYPE (PX), ITS GENOTYPE (GX) AND THE GENOTYPE (AND PHENOTYPE) OF ITS RELATIVES (ANCESTORS,  
progeny
ancestors
COLLATERAL RELATIVES AND PROGENY)

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(MACIEJOWSKI,1990)

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ORIGIN OF ANIMALS IN THE HERD (POPULATION) (MACIEJOWSKI I ZIĘBA – 1982)

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Males mated with females (their offspring) 

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- full siblings, with other females.

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- half-siblings 

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and unrelated individuals in the herd (in population)

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Estimating heritability - analysis of variance


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We estimate the average and variance for:

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for the whole population,

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for all groups of half-siblings,

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for all sibling groups.

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We rely on the analysis of:

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- half-sibling groups: cattle, sheep,


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- full sibling groups: poultry, pigs.

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Variation analysis of full-sibling groups, half-sibling groups, and overall variability of unrelated animals.

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HERD (POPULATION) VARIABILITY – OVERALL VARIABILITY, HALF-SIBLING VARIABILITY AND FULL-SIBLING VARIABILITY (MACIEJOWSKI I ZIĘBA – 1982)

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HERITABILITY OF TRAITS

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We are

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focusing, as usual, strategy for policy

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herd population variability, overall variability,

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half sibling variability and full sibling variability.

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Maciejewski and Ziemba 1982 

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Heritability varies depending on the type of trait. 

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The size of the indicator varies from 0 to 1 (or from 0 to 100%).

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We distinguish features:

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The heritability varies depending on the type of trait.

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- with a low index, their value ranges from 0.00 to 0.20 - these are the predominant traits related to reproduction (fertility and fertility of animals, laying),
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- with an average value of the index from about 0.25 to 0.40 - milk yield, daily gain, body weight at birth, egg weight,
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- with an increased heritability index - above 0.4, 
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these are, among others, such features as: protein and fat content in milk, backfat thickness, carcass length in pigs, t
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he surface of the "sirloin eye", 
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egg shell color in poultry, 
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wool thickness in sheep.

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Breeding progress

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can be defined as the difference
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 between the average value of a trait 
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in the progeny population compared to the average value in the parent population.
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The increase in the value of traits 

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achieved by improving environmental conditions is called non-genetic progress.

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Breeding progress 

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is considered to be
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 the difference 
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that has been achieved through breeding work.
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SELECTION EFFICIENCY
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The breeding progress achieved is 


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a measure of the effectiveness of selection.

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The amount of breeding progress (Δ G), and thus the effectiveness of selection, depends on:


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-	accuracy of breeding value assessment,
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-	selection intensity,

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-	genetic variation.
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BREEDING PROGRESS - MATHEMATICAL APPROACH


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A simplified formula for breeding progress 
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is as follows:

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Δ G = RS * h2 

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Where:
RS – selection difference expressed 
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(in units in which the feature is measured);
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 h2 – heritability 

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of the trait.

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HERITABILITY AND BREEDING PROGRESS

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Genetic variability existing in the herd (population) 

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has a significant impact on
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 the size of breeding progress,
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 in particular the value of heritability (h2) of a given trait in this herd.
 
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With the value of h2 equal to 1, the entire selection difference is "transferred" to
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the offspring in the form of an increase in the value of the trait. 

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Breeding progress will be equal to the size of the selection difference. 
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Of course, 
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the example is hypothetical 
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and for very few traits there is such a high heritability.
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With a heritability of 0.5, 

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the offspring 

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will outnumber the parent by 50% of the selection difference.

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On the other hand,


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 if the heritability of traits is zero, 
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breeding progress will be impossible.
If any of the terms of 
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the product is equal to zero, there will be no breeding progress. 
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The breeder may slightly influence the amount of genetic variation. 
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Using the appropriate mating system or introducing animals from outside to your herd. 
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However, it can significantly affect the accuracy of selection 
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(R - correlation between the breeding value and the phenotypic value. 
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This issue was presented earlier, 
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when assessing the breeding value.
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Reasons for the lack of breeding progress - selection limit:

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-	the limit of the physiological possibilities of animals;

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-	lack of genetic variation: attempts  to maintain genetic variation:

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-	through skilful crossbreeding,

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-	importing "breeding material" from outside.

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When conducting breeding work



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 - also starting breeding work, 
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we first need to know the size of genetic parameters in the herd in the population: 
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heritability of traits 
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and correlations between traits.

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Thank you for your attention.