Mating Systems

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Lecture 24
Mating Systems
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Inbreeding
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Inbreeding
-- Increases homozygosity (uniformity gt like
gametes , like individuals)
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Inbreeding
-- Disadvantages of Inbreeding --
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Inbreeding
-- Disadvantages of Inbreeding -- 1) inbreeding
exposes deleterious genes
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Inbreeding
-- Disadvantages of Inbreeding -- 1) inbreeding
exposes deleterious genes 2) inbreeding
depression --reduced performance due to
increased homozygosity, exposing genes
with negative effects
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Inbreeding
-- Disadvantages of Inbreeding -- 1) inbreeding
exposes deleterious genes 2) inbreeding
depression --reduced performance due to
increased homozygosity, exposing genes
with negative effects --high risk (complete
lines can be lost)
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Inbreeding depression

• Reduction in fitness in inbred individuals
• Juvenile survival
• Adult survival
• Mate acquisition
• Social dominance
• Fertility and Fecundity
• Growth

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Inbreeding depression

• Reduction in fitness in inbred individuals
• Proper development
• Disease resistance
• Resistance to environmental stresses
• Metabolic efficiency
• Sensory acuity

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Non-Inbred vs. Inbred Crested Wood Partridges at
the MN Zoo

• 8 reduction in egg volume
• 10 reduction in egg weight
• 20 reduction in hatch rate
• 51 reduction in 30 day survival
• Non-inbred birds have 41 fewer medical notes
  than their inbred counterparts!

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Line breeding
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Line breeding
-- mating system design to maintain a high degree
of relatedness of descendants to a particular
ancestor (mild form of inbreeding) --
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Line breeding
Generation A super star ? 1 B 1/2
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Line breeding
Generation A super star ? 1 B 1/2 ? 2
C 1/4
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Line breeding
Generation A super star ? 1 B 1/2 ? 2
C 1/4 ? 3 D 1/8
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Line breeding
Generation A super star ? 1 B 1/2 ? 2
C 1/4 ? 3 D 1/8
--Very quickly we lose the gene combinations that
defined the superstar.--
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Line breeding
A 1 B C D 1/2
a F
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Line breeding
A 1 B C D 1/2 2 E 1/2 1/8
a F
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Line breeding
A 1 B C D 1/2 2 E 1/2
1/8 3 F 1/2 1/4
a F
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Line breeding
A 1 B C D 1/2 2 E 1/2
1/8 3 F 1/2 1/4
a F
Note The relationship is high but F is
reasonably low.
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Cross Breeding
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Example of Crosses
PB2
PB1
F1



Backcross
Backcross
F2
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Cross Breeding
-- crossing of animals from different breeds --
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Cross Breeding
-- crossing of animals from different breeds
-- --Breed -- subpopulation of a species
inter se mated with the objective of
maintaining particular characteristics that
define the group.
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Differentiation in Breeds
1) Different objectives using artificial
selection
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Differentiation in Breeds
1) Different objectives using artificial
selection Example Holstein -- milk Hereford
-- beef Simmental -- dual purpose
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Differentiation in Breeds
2) Originate in different environments and
are influenced differently by natural
selection
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Differentiation in Breeds
2) Originate in different environments and
are influenced differently by natural
selection Example Brahman versus
Hereford
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Differentiation in Breeds
2) Originate in different environments and
are influenced differently by natural
selection Example Brahman versus Hereford heat
dissipation, Brahman cattle have less hair,
sweat versus pant, have smaller metabolic
organs, lower birth weights and thicker hides
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Differentiation in Breeds
Over time breeds come to represent different
reservoirs of genes
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Differentiation in Breeds
Over time breeds come to represent different
reservoirs of genes 1) different alleles
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Differentiation in Breeds
Over time breeds come to represent different
reservoirs of genes 1) different
alleles 2) different frequencies
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Differentiation in Breeds Growth Hormone Alleles
Angus Brahman allele 1.0 .30 A
0 .17 B 0 .38 C 0 .20 D
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Reasons for Crossbreeding

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Reasons for Crossbreeding
1) Complementarity -- combine breeds to take
advantage of the best characteristics for both
breeds
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Reasons for Crossbreeding
1) Complementarity -- combine breeds to take
advantage of the best characteristics for both
breeds 2) Method of migration of new genotypes
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Reasons for Crossbreeding
1) Complementarity -- combine breeds to take
advantage of the best characteristics for both
breeds 2) Method of migration of new
genotypes 3) Creating synthetic breeds --
combining breeds then inter se mating to form a
new breed
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Reasons for Crossbreeding
1) Complementarity -- combine breeds to take
advantage of the best characteristics for both
breeds 2) Method of migration of new
genotypes 3) Creating synthetic breeds --
combining breeds then inter se mating to form a
new breed 4) Rapid change in performance
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Reasons for Crossbreeding
Example 1969 -- less than 15 Simmental
bulls imported in the US
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Migrating New Genotypes
A B Generation
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Migrating New Genotypes
A B Generation A 1/2A 1/2B 1
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Migrating New Genotypes
A B Generation A 1/2A 1/2B 1 A
3/4A 1/4B 2
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Migrating New Genotypes
A B Generation A 1/2A 1/2B 1 A
3/4A 1/4B 2 A 7/8A 1/8B 3
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Migrating New Genotypes
A B Generation A 1/2A 1/2B 1 A
3/4A 1/4B 2 A 7/8A 1/8B 3 1 -
(1/2)tA (1/2)tB t
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Creating Synthetics
Example Brangus (3/8 Brahman and 5/8
Angus)
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Creating Synthetics
Example Brangus (3/8 Brahman and 5/8
Angus) Angus Brahman 1/2A 1/2B
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Creating Synthetics
Example Brangus (3/8 Brahman and 5/8
Angus) Angus Brahman 1/2A
1/2B Brahman 1/4A 3/4B
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Creating Synthetics
Example Brangus (3/8 Brahman and 5/8
Angus) Angus Brahman 1/2A
1/2B Brahman Angus 1/4A 3/4B 5/8A 3/8B ?
BRANGUS
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Computing Fractions
GH x Lab
(1/2) GH (1/2) Lab
(1) GH x (1/2) GH (1/2) Lab
(3/4) GH (1/4) Lab
(3/4) GH (1/4) Lab x (1/2) GH (1/2)
Lab
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Computing Fractions
(3/4) GH (1/4) Lab x (1/2) GH (1/2)
Lab What is the expected fraction of GH and Lab
genes in a progeny resulting from this mating?
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Computing Fractions
(3/4) GH (1/4) Lab x (1/2) GH (1/2)
Lab GH (¾) x (1/2) (1/2) x (1/2) 5/8 Lab
(1/4) x (1/2) (1/2) x (1/2) 3/8
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Rapid Change
Example Targhee and Finn
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Reasons for Crossbreeding
Targhee -- 1.1 lambs/ ewe 1.5 lambs/
ewe
6 generations
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Reasons for Crossbreeding
Targhee -- 1.1 lambs/ ewe 1.5 lambs/
ewe Finn -- 2.6 lambs/ ewe 2.1 lambs/
ewe
6 generations
1 generation (1/2F 1/2T)
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Reasons for Crossbreeding
Targhee -- 1.1 lambs/ ewe 1.5 lambs/
ewe Finn -- 2.6 lambs/ ewe 2.1 lambs/
ewe
6 generations
selection
1 generation (1/2F 1/2T)
cross breeding