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Single gene effects on behavior
- Relatively rare (as usually more than one gene involved in behavior) but relatively easy to study
- Eg. hygienic and non-hygienic honey bees: bacteria (American foul brood) that attacks bee larvae. Hygienic colonies worker bees will uncap a cell in the colony if dead larva or pups are remove the corpse, non-hygienic colonies workers do not.
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Types of transgenics
- "knockout" - a gene is removed or rendered inactive
- "knockin" a novel gene is inserted
- "conditional" the promoter for a gene is altered so that it can be switched on or of by the experimenter
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Polygenic effects
- Most phenotypic characters are not associated with a specific gene but are the result of numerous genes interacting (polygenic)
- These effects are far harder to study, because many genes may have a small but important effect on phenotype
- Do not follow Medalian laws of inheritance
- Lots of work currently being done on quantitative genomics to id important genes for growth, development and disease susceptibility
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Pleiotrophy
- Allele has more than one effect on the phenotype
- Yellow allele in Drosophila: slower at matting, yellow strips on the body
- Norm rather than the exception
- Change in one enzyme likely to affect several pathways and phenotypic characters
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Demonstrating genetic effects on behavior
- Approaches to demonstrate genetic effects on Behaviour all involve linking behavior variation to genetic differences
- 1. using "natural" behavioral variation
- 2. using selective breeding
- 3. Using strain differences
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Natural species-species behavioral variation
- Interbreed closely related species with different patterns of behavior to study genetic influences of behavior
- e.g. Nest-building behavior in love birds
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Selective breeding
- Separate behavioral variants from within a population
- Select specific individuals to breed and repeat selection process in each generation (temperament)
- Behavioral differences that respond to selective breeding must be due at least in part to the differences in the genotype
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Natural individual-individual variation
- Temperament (calm - reactive) in cattle is heritable
- Heritability of 0.4-0.5 have been reported
- Angus more temperamental than Herefords
- Braham cross more agitated during restraint than shorthorns
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Domestication
Process by which a population of animals become adapted to man and the captive environment by genetic changes occurring over generations and environmentally-induced developmental events reoccurring during each generation
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Genetic mechanisms influencing domestication
- Inbreeding
- Genetic drift
- Selection: artificial, natural, relaxation of natural selection
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Inbreeding
- Create random changes in gene frequency
- Small captive populations
- Decreased genetic variabilityy
- "inbreeding depression" - lowering fitness of vigor due to inbreeding: egg hatchability, clutch size, milk yield, litter size
- Increased risk of genetic disease
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Genetic drift
- Certain alleles become randomly fixed or lost
- Decrease genetic variability
- Becomes more severe and more important the smaller the breeding population is
- "Founder Effect" - When a population is bred from a few originators, genetic drift can be exceedingly severe, and alleles from one or two founders can dominate the resulting population: probably a common component of genetic disease in inbred populations, Known cause of behavior problems in show dogs.
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Side effects of selection
- Behavioral problems
- Physiological problems
- Immunological problems
- Production diseases: diseases caused by systems of management, feeding and breeding of high producing strains of animals
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Dairy cattle
- Selection for increase milk production
- Lower energy balance in high producers
- Higher incidence of metabolic disorders
- More days open
- Longer calving interval
- More service/conception
- More digestive problems
- More leg injuries
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The problem of pleiotropy
- Over-selection for desired traits can lead to pleiotropic selection for undesired traits
- Broiler chickens have been intensively selected for breast muscle mass growth, and muscle, carcass weight ratio: rapid growth, altered feeding behavior; altered weight distribution affects gait; growth of skeleton and internal organs does not keep up
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Pleiotropy and over selection
- Reduced cardiopulmonary capacity
- Cannot withstand much physical exertion, prone to stress-induced mortality as they age...
- ...so that breeding birds must be heavily food restricted in order to survive to sexual maturity
- Bone weaknesses, and diseases of - and injuries to - the legs
- A small proportion of birds may become too lame to reach food and water
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Pleiotropy and the selection environment
- Behavior is easily pleiotropically selected
- eg. selection for rapid growth of individuals can also lead to selection for aggression
- When these individuals are housed together aggression may be so severe that it hinders the average growth seen in the group
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Genomics/receptors
- Lots of work happening right now
- Gene for serotonin receptor HTR2C and feather damage
- SNPs (single nucleotide polymorphisms) in a number of genes mediation HPA (hypothalamic-pituitary adrenal) axis affects vasopressin receptor 1B and glucocorticoid receptors
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Future directions
- Molecular biology, gene editing
- What traditionally (be selective breeding) takes 8 generations (24 years in cows) can now be accomplished in a single generation by gene editing.
- We demonstrated that a sequence associated with horns in dairy cattle could be converted to a natural beef cattle variant that is hornless, providing a strategy to improve animal welfare by genetic instead of physical or chemical dehorning
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