Development of inbreeding and relationship under selection

1
Development of inbreeding and
relationship under selection
Moduel: Selection theory, design and optimisation of
breeding programs
Steffen Huchthausen Student-Nr. 21202474
Md Abu Bakar Siddik Student-Nr. 21435158

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Description of the problem
In animal-breeding some top sire are often used to produce a large
number of offspring. This will lead to the fact that the effective
population size Ne decreases very quickly and inbreeding
increases. Therefore a large number of problemes may arise if
inbreeding is continued over a long period in a population.

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„Inbreeding, the mating of individuals or organisms that are closely
related through common ancestry, as opposed to outbreeding,
which is the mating of unrelated organisms. Inbreeding is useful in
the retention of desirable characteristics or the elimination of
undesirable ones, but it often results in decreased vigour, size, and
fertility of the offspring because of the combined effect of harmful
genes that were recessive in both parents.“
(Encyclopædia Britannica 2017)
Defintion of inbreeding

4http://evolution.berkeley.edu/evolibrary/article/conservation_03

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Inbreeding Depression
Inbreeding depression as a consequence of
inbreeding, is the reduction of the mean
phenotypic value shown by characters connected
with reproductive capacity or physiological
efficiency.
(Falconer 2009)
Source: Biology notes for A level

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Inbreeding coefficient
The inbreeding coefficient of an individual is the average
probability that two genes at any given locus are identical by
descent. The average inbreeding coefficient of all individuals in a
population expresses the amount of drift in allelic frequencies
from a defined base population.
(Falconer 2009)
If inbreeding is the only source of disequilibrium, the inbreeding
coefficient (F) in a population for a given locus can be estimated
from the deviation between the expected (He) and observed
number (Ho) of heterozygotes.
F= (He – Ho) / He
(Groen 1995)

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Mean Kinship
Mean kinship is calculated by the kinship
(relatedness) of that animal with the entire
current population (including itself). Therefore
mean kinships per animal are relative to the
current population. This means that mean
kinship of a specific animal might change over
time when a population changes. For example
mean kinship will increase each time an animal
produces progeny.

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Relationship between Kinship and
inbreeding coefficient
Φii = Kinship coefficient
fi= inbreeding coefficient

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Illustration of the development of
inbreeding and kinship with
different paramters in R

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Explanation of the parameters
● Population size
● Number of generations
● Base population means
● Phenotypic variance = whether that trait has the
ability to respond to natural or artificial selection
and whether the trait can respond to
environmental changes

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● Heritability = estimates how much variation in a
phenotypic trait in a population is due to genetic
variation between individuals in that population
● Genetic correlation = is the proportion of
variance that two traits share due to genetic
causes
● Weights for trait1, trait2 in selection index
● Economic weights for trait1, trait2 in selection
goal
● Selection proportion

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Used standard parameters
● Population size (N) = 100
● Number of generations (N_gen) = 10
● Base population means for trait 1 & trait 2
(mu_g) = 0
● Phenotypic variance for trait 1 & trait 2
(var_p) = 1
● Heritability for trait 1& trait 2 (h2) = 0.3

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● Genetic correlation (rg) = 0.0
● Residual correlation (re) = 0.0
● Weights for trait 1in selection index (b) =1
● Weights for trait 2 in selection index (b) = 0
● Economic weights for trait 1 in selection goal
(w) = 1
● Economic weights for trait 2 in selection goal
(w) = 0

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Illustrations
Without selection
● Selection proportion = 1 (keep all)

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Without selection and h² = 0,7
● Selection proportion = 1 (keep all)

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Weak selection intensity
● Selection proportion = 0.75 (keep best 75%)

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Weak selection intensity and
h² = 0,7

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Strong selection intensity

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Strong selection intensity and
h² = 0,7

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Strong selection intensity and
h² = 0,7

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Conclusion
● The higher the selection intensity, the stronger
the increase in inbreeding and kinship
● A higher heritability of trait entails in a slower
increase of inbreeding and kinship

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Inbreeding in practical animal breeding
Hereford breed
● in the hereford breed a simple recessive defect of dwarfism was not just
propagated within the Hereford breed, but nearly brought the breed as a
whole to commercial irrelevance from the 1920’s to the 1960’s because of
continued inbreeding
● through much investigative work looking the “index”
animal was identified as a bull born in 1901
● that bull was used in the program for eight or nine years
● the results of this simple genetic defect went
undetected until the 1920’s and unrecognized
for what it was until the 1940’s
(Hartman 2014)
Source: Hartman

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Source: Changed after American Museum of Natural History

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Inbreeding in practical plant
breeding
Positive use in production of F1-
hybrids in maize
Source: Natur.de

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Continous self-fertilization lead to fully
homozygous plants called inbred lines.
Source: Biosciences for Farming in Africa

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If members of two inbred lines are mated,
the offspring display heterosis.
Source: Jun Cao & Ruth Swanson-Wagner, Iowa State University

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Heterosis-Effect
● The Heterosis effect is the particularly high
performance of hybrids
● It is the yield of the F1 minus the parental mean
Source: Ted Probert

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Heterosis is highest in the F1 generation and
declines thereafter
Source: Biosciences for Farming in Africa

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Sources
● Falconer, D. S. & T. F.C. Mackay, 2009: Introduction to quantative genetics.
● Groen, A. F., J. J. Eisen & B. W. Kennedy, 1995: Potential bias in inbreeding estimates
when using pedigree relationships to assess the degree of homozygosity for loci under
selection.
● Hartman, M., 2014: Breeding Matters III – Inbreeding vs. Line Breeding
(http://onpasture.com/2014/10/20/breeding-matters-iii-inbreeding-vs-line-breeding/),
visited on the 16.07.2017.
● The Editors of Encyclopædia Britannica, 2017: Inbreeding.
(https://www.britannica.com/science/inbreeding), visited on the 16.07.2017.
A. F. Groen 9 B. W. Kennedy 9 J.J. Eissen

Development of inbreeding and relationship under selection

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