1 / 43

Dominance, mating and crossbreeding

Dominance, mating and crossbreeding. Chapter 10. Mating. Mating is pairing selected sires and dams = comes after selection Mating determines how selected alleles combine within individuals Benefit from non-additive genetic effects. Mating strategies. Mating within populations

clement
Download Presentation

Dominance, mating and crossbreeding

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Dominance, mating and crossbreeding Chapter 10

  2. Mating • Mating is pairing selected sires and dams • = comes after selection • Mating determines how selected alleles combine within individuals • Benefit from non-additive genetic effects

  3. Mating strategies • Mating within populations • Which individuals to mate together? • Mating between populations • = crossbreeding • Which lines to cross with each other?

  4. Mating within populations • Affects genetic make-up of next generation of selection candidates • Does not affect long-term genetic improvement

  5. Major mating strategies • Random mating • Assortative mating • Mating based on family relationships • Mate selection

  6. Random mating • = Absence of any specific mating strategy • Mates chosen at random within selected sires and dams • NOT same as random selection!

  7. Assortative mating • Mating based on phenotypes or EBVs • Two types: • Positive assortative mating • Negative assortative mating

  8. Positive assortative mating • = Mating of similar individuals • Progeny? • More extreme •  Increases genetic variance (temporarily) • Practical use limited • Also need to mate poorer animals with other poorer animals!

  9. Negative assortative mating • = Mating of dissimilar individuals • Progeny? • More intermediate •  Decreases genetic variance (temporarily) • Compensatory/corrective mating • Aims to correct faults of parents in offspring • Dairy cattle

  10. stierenkaarten

  11. Mating on family relationships • Preferential mating of relatives • = Inbreeding • Avoidance of mating of relatives

  12. x Minimum kinship mating • Avoiding mating of relatives • Calculate coefficient of kinship for all possible combinations of sires and dams • Choose matings to minimise average coefficient of kinship • Postponesoccurrence of inbreeding • Reduces long-term rate of inbreeding

  13. x Minimize kinship mating in practice • In real life, minimum kinshipmating is complicated but canbedone • Manybreedingprogrammesusesomesort of mate selectiontorestrictkinship - avoidmatingsbetween close relatives • Full sibs • Half sibs • cousins

  14. Mate selection • Combines selectionandmating in a single step • Calculateexpectedprogeny performance foreverypossiblemating of candidates • Do matingswithhighestexpectedprogeny performance • Utilisesnon-additive geneticeffects but you have toknowthem.....

  15. Summary: Mating within… • …populations means deciding which sire to mate with which dam • You can benefit from • Corrections in phenotype • non-additive genetic effects • Main use: avoid highly inbred offspring • full sibs • half sibs • cousins

  16. Mating between populations • Mating between populations: • Used to produce final production animals • Pure production strategy, no effect on breeding population

  17. Crossbreeding • Breeding system where sires and dams originate from different lines • Lines within breed • Different breeds • Many ways to combine lines • Benefit as much as possible of heterosis • Breed complementarity • Common in pigs, chicken and beef cattle

  18. A tropical breed: Nelore short hair, skin folds, long ears, no body fat reserves, long legs

  19. A temperate breed: Red Agnus Coarse hair, subcutaneous fat, short stature

  20. corssbred: productive in tropical climate, high tick resistance! X

  21. Crossbreeding in dairy cattle • Crossbred (F1)between indigenous cattle and Holsteins perform well in a number of developing countries • Should crossbreeding be implemented? • Consider population with 100.000 F1-cows

  22. Crossbreeding in dairy cattle • Large pure-bred cow population needed for the production of F1-replacements. • Bottleneck: • Reproductive rate males: no problem • Reproductive rate females: very low • 1 offspring per year • 4 offspring during life time

  23. 100,000 F1 animals (Zebu*Holstein) • Parental breeds: • Holsteins: imported (semen) • Zebu: local pure-bred cow population • Replacements for F1 population? • Every year 25% of cows (F1 and purebred) replaced • 25,000 F1-heifers needed each year. • 50,000 Zebu cows need to be inseminated with Holstein semen. • 50,000 Zebu cows need to be inseminated with Zebu semen for maintaining Zebu population

  24. Crossbreeding between breeds: concluding remarks • In developing countries: • Quick fix: improved performance, • No long term genetic improvement! • Who maintains the local breed? • Only when the local breed serves a purpose!

  25. Time for a break

  26. Crossbreeding: Atlantic Salmon 25 ♀-Gaspe 25 ♀- Mowi 25 ♀-Laks Milt 15 ♂ Gaspe (CD) Mowi (NO) Laks (UK) eggs eggs eggs eggs eggs eggs eggs eggs eggs Crosses:

  27. Cross Breeding: salmon Ranking for GF3 from smolt to 4.5 kg The results of the SP tests are used to direct the crosses in future spawning's for production.

  28. Heterosis • Crossbred offspring is better than parent average • Also called hybrid vigour (plant breeding) • Caused by dominance (and epistasis) • “Specific combining ability of lines” • Can be expressed in trait units • HF1 = µF1 – ½(µsire + µdam) • Usually expressed as percentage • HF1 = 100% x (crossbred mean – parent mean) (parent mean)

  29. Example: Heterosis in salmon • Harvest weight • Mowi-line: harvest weight = 3.8 kg • Laks-line: harvest weight = 4.0 kg • Mowi x Laks F1: harvest weight = 4.1kg What is the heterosis? • HF1= 4.1 - ½(3.8 + 4.0) = 0.2 kg • HF1 % = 0.2 kg / 3.9 kg x 100% = 5.1%

  30. Genetic basis of heterosis • Crossbreeding leads to more heterozygotes if there is a difference in allele frequency () • Line1 = MM, line 2 = LL,  = 1 • F1 = ML = maximum heterosis • 1-locus: d > 0  F1 will be better than parent average = ML > (MM + LL)/2

  31. Example: Fillet% in Salmon • Line 1, p(M) = 0.8; Line 2, p(M) = 0.3 •  = 0.8 - 0.3 = 0.5 • GMM = 60%, GML = 64%, GLL = 65% • o = (65+60)/2 = 62.5% • d = 64 - 62.5 = 1.5% • HF1 = d x 2(eq 10.10) = 1.5 x 0.52 = 0.375 fillet%

  32. Heterosis: two types • Direct or individual heterosis • Maternal heterosis

  33. Breeding line D D dam line C sire line Breeding line C (♂ & ♀!) (♂ & ♀!) Selection on growth and meat quality CxD F1-offspring Selection on reproduction Production Population Crossbreeding: two-way scheme

  34. Two-way system • More uniform F1 production population • Breed/line complementarity • Heterosis in (CxD) progeny • Note: F1 animals are not used for pure line breeding! •  All selection within pure lines D and C

  35. Two-way system • Heterosis for growth (CxD) progeny? • Direct: growth • Maternal: -- • Hgr = 4% • Gr (C) = 700 g/d; Gr (D) = 680 g/d • Gr (CxD)= 1.04 x (700+680)/2 = 718 g/d

  36. Two-way system • Heterosis for litter size in (CxD) progeny? • Direct: vitality • Maternal: --! • Hgr = 4% (vitality) • nr Pl (C) = 10; nr Pl (D) = 11 • Nr Pl (CxD)= 1.04 x (11) = 11.44 Pl

  37. Line A Line C Line D F1 sow C×D Fattening pig A × (C × D) Crossbreeding: three-way scheme Selection & Replacement Selection & Replacement Selection & Replacement Selection on reproduction Selection on growth and meat quality

  38. Three-way system: heterosis • Direct: growth in (A x (CxD)) pigs • Mean parental lines? • (750 + ½(700+680))/2 • 1.04 x 720 = 749 g/d • Heterosis CxD is not heritable!!

  39. Three-way system: heterosis • What about litter size? • Direct: 4% (vitality of piglets) • Maternal: 6 % (nr of piglets born) • Mean litter size • A: 8 • C: 10 • D: 11

  40. Three-way system: heterosis • Litter size: parent mean • CxD ! • (10+11)/2 = 10.5 • Maternal H: 0.06 x 10.5 • Direct H: 0.04 x 10.5 • Sum: 10.5 + 1.05 = 11.55 PL

  41. Three-way system • Uniform end product (A x (CxD)); breed complementarity • Heterosis in (A x (CxD)) pigs • Maternal heterosis in (CxD) sows •  better reproduction • Protection of genetic material

  42. Line A Line C Line D F1 sow C×D Info Info Fattening pig A × (C × D) What is the breeding goal? Selection & Replacement Selection & Replacement Selection & Replacement Selection on growth & litter size Selection on growth, backfat and meat%

  43. Summary: Crossbreeding… • … = production strategy • Crossbred individuals are (usually) not parents • Crossbreeding itself does not contribute to G • Aims to benefit from heterosis & line complementarity • Genetic improvement within pure lines • Should aim at crossbred performance

More Related