This presentation has been supported by the Erasmus+ KA2
Cooperation Partnerships grant no. 2021-1-SK01-KA220-HED-000032068
“Innovation of the structure and content of study programs in the field of animal genetic and food resources management with the use of digitalisation
The European Commission support for the production of this presentation does not
constitute an endorsement of the contents which reflects the views only
of the authors, and the Commission cannot be held
responsible for any use which may
be made of the information contained therein
This presentation
has been created
by Stanislav Socha
professor at
Siedlce
University
Institute of Zootechnic and Fisheries.
The topic will be concerning sources of variation in the population,
as well as genetic and environmental variability.
Phenotype, genotype
and environment
The value of the phenotype
depends on the genotypic value of the individual
influence of environmental conditions.
Characteristics important in animal husbandry include traits
related to the performance of animals, e.g.
milk yield, animal reproduction and health.
Generally, the features can be classified into two groups
quality features and quantitative characteristics of
group, etc..
Quantitative features and qualitative features
The main factor
differentiating these two groups of features is the number of pairs of alleles
also called genes affecting their shape and the number
of classes of differentiated phenotypes.
In the case of qualitative traits,
the number of pairs of genes or a series of alleles
influencing their formation is limited and varies
within quite narrow limits from 1 to a maximum of 2 to 4.
This, in turn affects a limited number of genotypes.
Hereditary assumptions of individuals and as a result individuals with specific phenotypes.
All the characteristics of the organism.
for examples
of quality characteristics include
animal color, row, feather color in poultry,
horned or polled cattle, sheep and goats.
Blood groups systems.
In the case of features defined as quantitative.
The situation is much more complex.
Firstly, the number of genes polygons
affecting their shape is very numerous, sometimes difficult to determine.
Then, in addition to genetic assumptions,
environmental factors have a significant impact on their formation.
This type of inheritance not only significantly increases the diversity of individuals in the herd,
but also makes it extremely difficult to identify genotypes
based on phenotype.
HERITABILITY OF TRAITS
With the multiplicity of factors affecting traits.
It is impossible to determine the contribution of a single gene to the formation of a quantitative trait.
Only statistical methods allow to determine the influence of genotype
and environment on the variability of the trade in the herd population.
And to estimate the heritability
of the traits of interest on this basis.
It is the variation in the value
or quality of traits observed among individuals in a herd.
In a population.
Genetic variation is the basis for the genetic improvement of animals.
Its sources are.
Recombination leads to the formation of different new genotypes,
and mutations lead to the formation of new genes.
Other systems within a chromosome or between chromosomes.
According to Jeżewska-Witkowska , 2010.
The three main reasons for variability are aesthetic-
diversity of forms in nature, material nature-
A variety of products is necessary to meet your needs and improvement-
Thanks to the variability the breeder can select the best animals
for a given trait for further breeding.
In animal husbandry, knowledge of genetics can prove quite useful,
as it can help with improvement of animals, production planning for market needs.
For example, coat color marking color of subcutaneous fat.
Color of shell in animal reproduction,
predicting their vitality, temperament and physique.
The possibility of avoiding defects and diseases of genetic origin,
creating lines of laboratory animals for the needs
of human
medicine
Variability of quantitative features and selection difference
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)
(MACIEJOWSKI,1990)
ORIGIN OF ANIMALS IN THE HERD (POPULATION) (MACIEJOWSKI I ZIĘBA – 1982)
Males mated with females (their offspring)
- full siblings, with other females.
- half-siblings
and unrelated individuals in the herd (in population)
Estimating heritability - analysis of variance
We estimate the average and variance for:
for the whole population,
for all groups of half-siblings,
for all sibling groups.
We rely on the analysis of:
- half-sibling groups: cattle, sheep,
- full sibling groups: poultry, pigs.
Variation analysis of full-sibling groups, half-sibling groups, and overall variability of unrelated animals.
HERD (POPULATION) VARIABILITY – OVERALL VARIABILITY, HALF-SIBLING VARIABILITY AND FULL-SIBLING VARIABILITY (MACIEJOWSKI I ZIĘBA – 1982)
HERITABILITY OF TRAITS
We are
focusing, as usual, strategy for policy
herd population variability, overall variability,
half sibling variability and full sibling variability.
Maciejewski and Ziemba 1982
Heritability varies depending on the type of trait.
The size of the indicator varies from 0 to 1 (or from 0 to 100%).
We distinguish features:
The heritability varies depending on the type of trait.
- 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),
- with an average value of the index from about 0.25 to 0.40 - milk yield, daily gain, body weight at birth, egg weight,
- with an increased heritability index - above 0.4,
these are, among others, such features as: protein and fat content in milk, backfat thickness, carcass length in pigs, t
he surface of the "sirloin eye",
egg shell color in poultry,
wool thickness in sheep.
Breeding progress
can be defined as the difference
between the average value of a trait
in the progeny population compared to the average value in the parent population.
The increase in the value of traits
achieved by improving environmental conditions is called non-genetic progress.
Breeding progress
is considered to be
the difference
that has been achieved through breeding work.
SELECTION EFFICIENCY
The breeding progress achieved is
a measure of the effectiveness of selection.
The amount of breeding progress (Δ G), and thus the effectiveness of selection, depends on:
- accuracy of breeding value assessment,
- selection intensity,
- genetic variation.
BREEDING PROGRESS - MATHEMATICAL APPROACH
A simplified formula for breeding progress
is as follows:
Δ G = RS * h2
Where: RS – selection difference expressed
(in units in which the feature is measured);
h2 – heritability
of the trait.
HERITABILITY AND BREEDING PROGRESS
Genetic variability existing in the herd (population)
has a significant impact on
the size of breeding progress,
in particular the value of heritability (h2) of a given trait in this herd.
With the value of h2 equal to 1, the entire selection difference is "transferred" to
the offspring in the form of an increase in the value of the trait.
Breeding progress will be equal to the size of the selection difference.
Of course,
the example is hypothetical
and for very few traits there is such a high heritability.
With a heritability of 0.5,
the offspring
will outnumber the parent by 50% of the selection difference.
On the other hand,
if the heritability of traits is zero,
breeding progress will be impossible. If any of the terms of
the product is equal to zero, there will be no breeding progress.
The breeder may slightly influence the amount of genetic variation.
Using the appropriate mating system or introducing animals from outside to your herd.
However, it can significantly affect the accuracy of selection
(R - correlation between the breeding value and the phenotypic value.
This issue was presented earlier,
when assessing the breeding value.
Reasons for the lack of breeding progress - selection limit:
- the limit of the physiological possibilities of animals;
- lack of genetic variation: attempts to maintain genetic variation:
- through skilful crossbreeding,
- importing "breeding material" from outside.
When conducting breeding work
- also starting breeding work,
we first need to know the size of genetic parameters in the herd in the population:
heritability of traits
and correlations between traits.
Thank you for your attention.