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Hello. Domestication, evolution, and breeding.

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What do they have in common? Everything. 
Everything is essentially evolution.

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The lecture is part of Module 3, Animal Breeding. 
The creation of this presentation was supported

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by the ERASMUS+ KA2 grant within the ISAGREED 
project, Innovating the content and structure

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of study programs in the field of animal genetic 
and food resources management using digitization.

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Domestication is an evolutionary process 
in which the influence of humans weakens

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the effects of many natural selection factors 
(although they still exist). Humans began using

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selective breeding to change desired traits 
and their values. The effects of selection

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also affected related traits. At the same time, 
humans controlled movement, feeding, and other

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factors that, along with breeding, influenced 
the development of domesticated animal forms.

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Breeding is an evolutionary process in which 
humans are the driving force behind changes

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in traits. Humans define goals for breeding and 
select only the best individuals with desired

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trait values. Typical goals for breeding are 
combinations of different trait values that

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are important for production. We want to change 
the average value of traits in a population in

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the desired direction. The main problem is 
that most production traits have a complex,

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quantitative nature (P is influenced by genotypes 
of many genes and environments), so breeding must

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be based on knowledge of the genetic structure 
of the population and environmental conditions.

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We start from the basic breakdown of phenotypic 
variability, which is composed of genetic

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variability and environmental variability.
Genetic variability in a population is

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characterized by the heritability coefficient, 
which is the proportion of genetic variability

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to the total phenotypic variability. In other 
words, heritability tells us to what extent

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phenotypic differences among individuals in a 
population are caused by genetic differences.

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Animal breeding is based on these hypotheses:

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The subject of evolution/breeding is 
not the individual, but the population.

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Most utility traits are determined by polygenes 
– typical for quantitative traits. Genotypes,

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not genotypes, are transmitted from generation to 
generation through genes (alleles) via gametes,

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which combine to create new genotypes in 
the offspring generation. The phenotype of

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quantitative traits in individuals is modified 
by environmental influences: P = G + E.

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The amount of genetic improvement (ΔG) 
and its reflection in economic efficiency

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(financial gain) depends on: The genetic 
basis of traits and their variability in

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the population (the value of heritability of a 
given trait in the population must be known);

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Estimation of breeding values of individuals and 
populations (genetic value of an individual),

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and the accuracy of defining breeding goals.

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Ultimately, everything depends on the optimal 
utilization of animals with high breeding values

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or the optimal dissemination of the genes 
of this individual into next generations.

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What information is needed in breeding? Phenotypic 
data - Utility; Genetic (genotypic/genomic) data

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(Kinship relations, Genotypes of genetic 
markers) and the use of statistical methods

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to link data and analyze to 
determine the genetically

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superior individual (best alleles -> 
offspring, for a given environment).

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The decisive problems in breeding that are 
addressed are defining a realistic breeding goal,

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choosing a suitable strategy, utilizing 
data that explain phenotypic variability,

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identifying genetically superior 
individuals through genetic analysis,

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and selecting and passing on genes to the 
next generation using reproductive methods.

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The genetic evaluation system helps optimize 
breeding programs. Roughly 100 years ago,

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selection was based on phenotype and 
genetic progress was not as clear-cut.

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The reason was that utility traits are of a 
quantitative nature and have complex inheritance.

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Phenotypically valuable individuals may not have 
been genetically superior but may have developed

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in better conditions. After understanding 
how inheritance works and the development

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of population genetics and quantitative 
traits in the first half of the 20th century,

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we can speak of genotype-based selection, in 
other words, based on estimated breeding values,

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practically since the 1950s.
This reason can be seen in

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the diagram of the principles of genetic 
improvement through selection. We start

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with the original population from which we want 
to select the genetically superior individuals.

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We use a certain degree of selection intensity, 
which is influenced by selection differential d

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and phenotypic variance (standard deviation 
sigma P). We also need to know the estimated

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heritability value (essentially genetic 
variance) as accurately as possible.

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If a trait has high heritability, meaning there 
are large genetic differences between individuals,

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then with high selection intensity, I select 
parents with the best alleles in the given

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environment, and by transferring them to the next 
generation, I can expect the difference between

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the average of the new generation of offspring 
and the original generation from which the parents

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were selected (genetic gain delta G) to change in 
the desired direction and with significant value.

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For traits with low heritability 
(e.g. reproductive traits),

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more intense selection does 
not increase genetic gain

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much because there are small genetic 
differences among individuals in the population.

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A breeding equation has been developed, where 
genetic gain equals selection intensity times

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the accuracy of breeding value estimation 
times additive genetic standard deviation.

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If we divide it by the generation 
interval, we obtain genetic gain per year.

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The genetic value of an individual cannot 
be directly determined, so estimates

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of genetic differences between evaluated 
individuals, i.e. breeding values, are used.

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This is the genetic deviation in performance 
traits from the average of contemporary

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group (individuals living in the same 
conditions as the evaluated individual).

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We must realize that with sexual reproduction, 
inheritance occurs through the gametes of parents,

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and gametes do not contain both alleles 
of the genotype, only one allele.

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Therefore, breeding value is the value of allele 
effects transmitted from parents to offspring.

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Methods for estimating breeding value are 
mathematical-statistical processes for

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purifying genetic influences affecting utility 
traits from non-genetic influences (environment).

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The simplest expression of estimated 
breeding value based on individual

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utility is the phenotypic difference 
multiplied by heritability. The

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estimated breeding value is then not 
phenotypic but genetic deviation.

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An example for explanation. We have a 
bull with a weight of 350 kg at one year,

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the population average was 300 kg.

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Its phenotypic deviation is +50 kg. The question 
is, is this phenotypic deviation caused only by

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genetic differences, i.e. is it really genetically 
superior to other individuals in the population?

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The bull could be good based on its genes, but 
also because it developed in better conditions.

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Therefore, it is necessary to estimate breeding 
value as genetic deviation in order to decide

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which individual to use as parents to 
pass on alleles to the next generation.

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In another example, we compare 
two individuals, Karel and Rudolf.

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And even though we see that 
Karel has a greater weight

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and our ancestors would probably choose him 
as a stud (based on phenotype), today, when

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selection is based on genotype (based on breeding 
value), we would choose Rudolf as the genetically

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superior individual, who is compared to another 
group of peers but with the same heritability.

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In conclusion: The main method of breeding 
and evolution in general is selection. The

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goal of genetic evaluation of individuals is 
to determine genetically superior individuals

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with the highest breeding values; It is based 
on population variability and heritability for

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a specific trait; Select individuals with the 
most suitable alleles for the given conditions

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as parents; By intentional reproduction, 
transfer their alleles to the next generation;

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Expect a shift in the average value of the 
bred trait in offspring (genetic gain);

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Breeding must generate economic profit.
And thank you for your attention.