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Hello everyone, I welcome you to the following
lecture from the Conservation module on Sustainable

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Use of Animal genetics, the topic of which
is Fundamentals of Genetic Variability Assessment

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in Animal genetic resources.

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In general, we can say that genetic variability
is the basis of all breeding programs and

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procedures.

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By the term genetic variability, we mean the
variability of the alleles and genotypes that

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manifests itself in the monitored population.

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The essence of genetic variability is genetic
polymorphism.

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Since the basis of genetic polymorphism is
the variability of alleles at one locus, the

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genetic variability of the population is conditioned
precisely by the existence of genetic polymorphisms.

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Due to their variability, genetic polymorphisms
change the evolutionary potential of populations

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because these populations can respond to short-term
selection pressures.

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Among the effects affecting the genetic variability,
we include:

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Historical and current population size.

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Population size significantly affects genetic
variability.

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There is a significant loss of genetic variability
in small, often closed populations.

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Another effect is the Bottleneck Effect.

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It is because, with a substantial reduction
in the number of individuals in the population

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in the past, there is a reduction in the size
of genetic variability, which, without the

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migration of new genetic variability nor an
increase in the number of individuals in the

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population, will not increase genetic variability.

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Also, breeding programs, through the selection
of parental pairs, limit the amount of genetic

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variability.

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During these reasons, natural selection reduces
the value of genetic variability too.

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Furthermore, as already mentioned, mutation
and migration between populations increase

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the amount of genetic variability.

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Last but not minor, genetic variability is
influenced by the interaction between all

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the mentioned factors.

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Multiple allelic sets of alleles of many genes
and genetic polymorphism ensure genetic variability

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in the population.

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Genetic variability in populations arises
with the help of positive mutations maintained

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and strengthened in the population by means
of natural or artificial selection.

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Genetic variability is primarily due to a
large amount of genetic information (genetic

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polymorphism) encoded in DNA molecules, which
is present in cell nuclei in the form of chromosomes.

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The value of genetic variability can be determined
using pedigree or molecular genetic methods.

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Among the pedigree analyses, we include indicators
of completeness of pedigrees, Indicators derived

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from a common ancestor and Indicators of the
probability of origin of genes.

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Among the molecular genetic methods describing
the level of genetic variability, we include

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the polymorphic information index, Expected,
and observed heterozygotes and Wright's fixation

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indices.

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However, the most basic indicators of genetic
variability we include the inbreeding coefficient,

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the relatedness coefficient, and the effective
population size.

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These indicators can be used both in pedigree
and molecular genetic methods.

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One of the important pedigree parameters is
the so-called completeness of pedigree.

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It is a basic parameter for the study of genetic
variability because the level of completeness

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of pedigree records determines the accuracy
of the estimated following parameters.

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It is expressed as a percentage representation
of known ancestors in each generations.

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The higher the values of the percentage drowning
of ancestors in most generations, the higher

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the accuracy of the other analysed coefficients.

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Among the indicators derived from the common
ancestor are the coefficient of inbreeding,

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coefficient of relatedness and effective population
size.

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The inbreeding coefficient quantifies the
value of inbreeding as the probability that

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two alleles on a chromosome locus are identical
by descent (IBD, or autozygous).

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Autozygosity is defined as the state of one
locus where two alleles are identical by descent.

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That is, they come from the same ancestor.

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Furthermore, we also recognize alleles that
are identical according to status, that means

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that the genotype is, for example, homozygous
dominant, but the alleles were obtained from

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different ancestors.

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Here, in the given example, one from individual
1 and the other from individual 2.

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In the second example, we also have homozygous
dominant, but he obtained both alleles from

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one ancestor – individual 3, so these are
autozygous alleles, or alleles identical by

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descent.

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Another parameter is the relationship coefficient,
which is the correlation between the genetic

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value (additive) between two individuals (correlation
between the genetic foundation of two individuals).

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We can obtain the kinship coefficient based
on the above relationship or formula, where

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n represents the number of paths from individual
X and Y to a common ancestor.

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In the connection, the inbreeding coefficient
of the common ancestor of individuals X and

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Y is also considered.

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Another coefficient that can be used to evaluate
genetic variability in a population is the

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effective size of the population.

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This coefficient estimates the number of unrelated
animals that in an ideal population (so-called

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panmictic population) would lead to the same
loss of genetic variability – that is, an

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increase to the same increase in the coefficient
of inbreeding from generation to generation

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as recorded in the analysed population.

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For example, according to the FAO, if the
effective population size is lower than 50

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individuals, it is a threatened population,
even if the given population may have thousands

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of individuals.

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Indicators of the probability of origin of
genes include Effective Number of Founders,

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Effective Number of Ancestors and Effective
Number of Founder Genomes.

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Under the term effective number of founders,
we can imagine the number of equally contributing

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founders - individuals with an unknown parents
they can create the same genetic variability

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as the monitored population.

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Under the term effective number of ancestors,
we can imagine the number of equally contributing

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ancestors (not founders) who can explain the
same genetic variability as a given population.

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This parameter is explained by the possible
recent decreasing of individuals in pedigree,

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or so-called the bottleneck effect, and partially
explains the loss of genetic diversity in

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the monitored population.

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The effective number of founders with the
non-random loss of founders alleles that would

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be explained to produce the same genetic diversity
as in population under study.

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The indicators shown on the previous slide
use the principles by which it is possible

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to maintain a sufficient level of genetic
variability.

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Among these principles is maximising the conservation
of genetic variability within a closed population

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by mating an equal number of offspring from
each basic ancestor.

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Furthermore, many pods minimise the random
loss of genetic variability.

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The equal representation of basic ancestors
in offspring generations reinforces the genetic

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variability found in each basic ancestor that
has yet to be eliminated from the progeny

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population if additional alleles of the basic
ancestors are present in multiple individuals.

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Among the molecular genetic methods of assessing
genetic variability are the polymorphic information

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index, which is stated as a criterion of variability
(or informability) of the analysed loci and

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which is mainly used in studies dealing with
linkage disequilibrium.

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A better method is to compare expected and
observed heterozygosity.

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This method studies intra-population variability
and the state, or level, of the inbreeding

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coefficient in the population.

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Based on the ratio of these two quantities,
the loss or increase of variability in the

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population is calculated.

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Another method is the so-called Wright's fixation
coefficients.

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These parameters compare the loss of genetic
variability at the individual, subpopulation,

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and whole population levels.

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This includes the loss of genetic variability
of an individual relative to a subpopulation,

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the loss of genetic diversity of an individual
relative to the whole population, and the

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differentiation of gene similarity between
subpopulations, which in the narrow sense

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of the word is taken as a fixation index and
quantifies the degree of genetic difference

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between populations.

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If the value of Fst is lower than 0.05, the
two subpopulations are genetically identical,

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and above the level of 0.125, the populations
are genetically different.

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This presentation introduced the basic principles
of assessing genetic variability based on

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pedigree and molecular genetic data.

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Thank you for your attention, and I look forward
to meeting you at the following lectures.