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Chapter 9: Inbreeding and cross-breeding Effect of inbreeding on individual and population level Effect of cross-breeding Minimum inbreeding systems Population.

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Presentation on theme: "Chapter 9: Inbreeding and cross-breeding Effect of inbreeding on individual and population level Effect of cross-breeding Minimum inbreeding systems Population."— Presentation transcript:

1 Chapter 9: Inbreeding and cross-breeding Effect of inbreeding on individual and population level Effect of cross-breeding Minimum inbreeding systems Population structure

2 Inbreeding depression decrease in the level of the production traits due to inbreeding Genes with dominance have most effect on the heterozygotes Increased level of homozygosity is the under laying factor which causes the inbreeding depression Genotype AA Aa aa Frequency p 2 + pqF 2pq - 2pqF q 2 + pqF

3 Linearity of the inbreeding depression Linear fall in daily slaughter gain in swine

4 Hybrid Vigour Increase in the level of production traits, due to crossing, is called hybrid vigour or heterosis Genes with dominance causes most effect on the heterozygotes Increased heterozygosity is the under laying factor which causes hybrid vigour

5 Effect of crossing Cannot be predicted Trial and error principle Good crossing-combinations can be repeated again and again

6 Crossing systems Two-way, three-way, four-way, back, or rotation crossing

7 Effect of crossing: Example

8 Calculation of hybrid vigour in sows: Example litter size Landrace  Yorkshire  11 Pure bred  10 Hybrid vigour = ( )/10 = 10 %

9 Crossing demands a surplus of females An RDM or SDM cow bears in average only 1.1 to 1.2 heifer calf, which is sufficient to maintain the pure bred population. Therefore, crossing production is not possible in these breeds, if pure breeding is desirable in the entire population

10 Negative recombination effects in F 2 Biochemistry in a two-gene system, which can be actual in F 2 individuals after a crossing of aabb x AABB

11 Inbreeding Pure breeding Line Breeding Crossing Breeding systems, summary

12 Pedigree Selected animals gets the same number of offspring Circular mating systems Minimum inbreeding systems

13 Mating of non-related (far out related) individuals Ca. 3-4 generations Necessary to maintain pedigree in pure breeding Pedigrees

14 All individuals gets two offspring Distribution of offspring after random mating

15 Circular mating systems

16 Breeding pyramid Gene flow between the different levels of herds


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