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Lecture 24

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.

Solomon
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Lecture 24

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  1. Lecture 24 Mating Systems

  2. Inbreeding

  3. Inbreeding -- Increases homozygosity (uniformity => like gametes , like individuals)

  4. Inbreeding -- Disadvantages of Inbreeding --

  5. Inbreeding -- Disadvantages of Inbreeding -- 1) inbreeding exposes deleterious genes

  6. Inbreeding -- Disadvantages of Inbreeding -- 1) inbreeding exposes deleterious genes 2) inbreeding depression --reduced performance due to increased homozygosity, exposing genes with negative effects

  7. 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)

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

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

  10. 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!

  11. Line breeding

  12. Line breeding -- mating system design to maintain a high degree of relatedness of descendants to a particular ancestor (mild form of inbreeding) --

  13. Line breeding Generation A “super star”  1 B 1/2

  14. Line breeding Generation A “super star”  1 B 1/2  2 C 1/4

  15. Line breeding Generation A “super star”  1 B 1/2  2 C 1/4  3 D 1/8

  16. 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.--

  17. Line breeding A 1 B C D 1/2 aF

  18. Line breeding A 1 B C D 1/2 2 E 1/2 1/8 aF

  19. Line breeding A 1 B C D 1/2 2 E 1/2 1/8 3 F 1/2 1/4 aF

  20. Line breeding A 1 B C D 1/2 2 E 1/2 1/8 3 F 1/2 1/4 aF Note: The relationship is high but F is reasonably low.

  21. Cross Breeding

  22. Example of Crosses PB1 PB2 F1 × × × Backcross Backcross F2

  23. Cross Breeding -- crossing of animals from different breeds --

  24. 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.

  25. Differentiation in Breeds 1) Different objectives using artificial selection

  26. Differentiation in Breeds 1) Different objectives using artificial selection Example: Holstein -- milk Hereford -- beef Simmental -- dual purpose

  27. Differentiation in Breeds 2) Originate in different environments and are influenced differently by natural selection

  28. Differentiation in Breeds 2) Originate in different environments and are influenced differently by natural selection Example: Brahman versus Hereford

  29. 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

  30. Differentiation in Breeds Over time breeds come to represent different reservoirs of genes:

  31. Differentiation in Breeds Over time breeds come to represent different reservoirs of genes: 1) different alleles

  32. Differentiation in Breeds Over time breeds come to represent different reservoirs of genes: 1) different alleles 2) different frequencies

  33. Differentiation in Breeds Growth Hormone Alleles Angus Brahman allele 1.0 .30 A 0 .17 B 0 .38 C 0 .20 D

  34. Reasons for Crossbreeding

  35. Reasons for Crossbreeding 1) Complementarity -- combine breeds to take advantage of the best characteristics for both breeds

  36. Reasons for Crossbreeding 1) Complementarity -- combine breeds to take advantage of the best characteristics for both breeds 2) Method of migration of new genotypes

  37. 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

  38. 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

  39. Reasons for Crossbreeding Example: 1969 -- less than 15 Simmental bulls imported in the US

  40. Migrating New Genotypes A × B Generation

  41. Migrating New Genotypes A × B Generation A × 1/2A + 1/2B 1

  42. Migrating New Genotypes A × B Generation A × 1/2A + 1/2B 1 A × 3/4A + 1/4B 2

  43. Migrating New Genotypes A × B Generation A × 1/2A + 1/2B 1 A × 3/4A + 1/4B 2 A × 7/8A + 1/8B 3

  44. 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)t]A + [(1/2)t]B t

  45. Creating Synthetics Example: Brangus (3/8 Brahman and 5/8 Angus)

  46. Creating Synthetics Example: Brangus (3/8 Brahman and 5/8 Angus) Angus Brahman 1/2A 1/2B

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