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Lecture 24. Mating Systems. Inbreeding. Inbreeding. -- Increases homozygosity (uniformity => like gametes , like individuals). Inbreeding. -- Disadvantages of Inbreeding --. Inbreeding. -- Disadvantages of Inbreeding -- 1) inbreeding exposes deleterious genes. Inbreeding.

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Lecture 24

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Lecture 24

Mating Systems


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Inbreeding


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Inbreeding

-- Increases homozygosity (uniformity => 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

GenerationA“super star”

1B1/2


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Line breeding

GenerationA“super star”

1B1/2

2C1/4


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Line breeding

GenerationA“super star”

1B1/2

2C1/4

3D1/8


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Line breeding

GenerationA“super star”

1B1/2

2C1/4

3D1/8

--Very quickly we lose the gene combinations that defined the superstar.--


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Line breeding

A

1BCD1/2

aF


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Line breeding

A

1BCD1/2

2E1/2 1/8

aF


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Line breeding

A

1BCD1/2

2E1/2 1/8

3F1/2 1/4

aF


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Line breeding

A

1BCD1/2

2E1/2 1/8

3F1/2 1/4

aF

Note:The relationship is high but F is reasonably low.


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Cross Breeding


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Example of Crosses

PB1

PB2

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

AngusBrahmanallele

1.0.30A

0.17B

0.38C

0.20D


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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 ×BGeneration


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Migrating New Genotypes

A ×BGeneration

A ×1/2A + 1/2B1


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Migrating New Genotypes

A ×BGeneration

A ×1/2A + 1/2B1

A ×3/4A + 1/4B2


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Migrating New Genotypes

A ×BGeneration

A ×1/2A + 1/2B1

A ×3/4A + 1/4B2

A ×7/8A + 1/8B3


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Migrating New Genotypes

A ×BGeneration

A ×1/2A + 1/2B1

A ×3/4A + 1/4B2

A ×7/8A + 1/8B3

[1 - (1/2)t]A + [(1/2)t]Bt


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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)

AngusBrahman

1/2A 1/2B


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Creating Synthetics

Example:Brangus (3/8 Brahman and 5/8 Angus)

AngusBrahman

1/2A 1/2BBrahman1/4A 3/4B


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Creating Synthetics

Example:Brangus (3/8 Brahman and 5/8 Angus)

AngusBrahman

1/2A 1/2BBrahmanAngus1/4A 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


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