Domestication and selection for production traits Flashcards
What is domestication?
- the process by which a population of animals becomes adapted to man and to the captive environment by some combination of genetic changes occurring over generations and environmentally induced developmental events recurring during each generation
What does domestication not assume about genes and the environment?
- does not assume that the genes and the environment operate independently
What does the domestication principle assume about the captive environment?
- assumes that the captive environment is different from the wild ancestral environment
- and that these differences are consistent over generations = allowing evolutionary forces to change the gene pool
How can humans accelerate changes in phenotype (that might not occur in nature)?
- by artificial selection or gene transfer
What was Belyaev’s fox experiment selection objective?
- tame response to humans in a series if handling tests
What concept of selection did Belyaev use?
- concept of destabilizing/disruptive selection
What were the correlated responses to selection for tame foxes?
- earlier opening of eyes and response to sound
- later fear response
- delayed rise in cortisol production
- white coat marks (8 generation)
- floppy ears, shorter wider muzzle
- earlier sexual maturity, larger litter, some out of season breeding
What common changes have we seen in domestic species?
- reduced brain size
- increased reproduction/ out of season
- decreased fearfulness of humans
- increased social motivation
What would help reduce stress in domesticated species?
- selection for reduction in defensive behaviour
What has an adaption to a safe environment caused for domestic species?
- little opportunity for perceptual and locomotory stimulation
- frequent invasion of personal space with little opportunity to escape from dominant individuals
- frequent association with humans
What is the most important consequence of domestication?
- reduced emotional reactivity to fear-evoking stimuli or environmental change
Less reactive animals can be handled with greater ease and what does this tend to lead to?
- reduced levels of stress in captivity
- higher levels of growth and reproductive performance
Genetic selection with species could affect welfare (especially in enhanced productivity animals) through the development of what?
- development of physical problems
- health problems associated with enhanced production
- modification of behaviour/threshold to stress
What physical issues can be seen as a result of genetic selection in cattle and poultry?
- poultry = rapid growth and bone weakness
- cattle = hypertrophy
Cattle with higher genetic merit for production often have lowered disease resistance - what issues can this cause?
- mastitis
What welfare issues are arising from selection for productivity in broilers?
- lameness
- ascites
- sudden death
What welfare issues are arising from selection for productivity in hens?
- feather pecking
What welfare issues are arising from selection for productivity in dairy cattle?
- reduced fertility and longevity
- increased lameness, metabolic problems, mastitis
What welfare issues are arising from selection for productivity in pigs?
- tail biting
- sow appetite
- fat reserves and fertility
How is temperament defined?
- as consistent individual differences in behaviour, particularly in reaction to fear of humans
Temperament offers a comprehensive view of behaviour and emphasises what?
- emphasises the individuals reaction to environmental challenge and change
Why should temperament be taken into account for both farm and zoo environments?
- farm = ability to cope with husbandry systems
- zoo = ability to cope and reproduce in captivity
Ewes with a calm temperament as more likely to show what at lambing?
- better maternal behaviour
- less avoidance of humans at lambing time
- quicker to return to lambs
- more time grooming lambs after birth
- more time at the birth site
- vocalised more
- lower lamb mortality
What can genetic variation in performance be due to?
- to a mix of individual genetic effects and genetic effects of social integration
There are two views of the source of selectable genetic variation - what are these and what do they each look at?
- traditional model = direct effect of genes
- social group model = direct effects + indirect genetic effects
There are two ways that group selection can be done - what are these?
- select the best group
- kin/family selection
What would you select the best group (in group selection) to combine?
- individual performance
- social/behavioural traits
How would kin/family selection work if you were to use chickens and laying performance?
- compare mean laying performance of cages of 9-12 birds
- include a measure of longevity
- selection and control lines
What is quantitative trait locus?
- selection of chromosome associated with a trait of interest
How can the chromosome associated with the trait if interest be identified?
- can be identified in animals by gene markers
- may be a gene or genes
- or genetic variant linked to a nearby gene
When selecting a chromosome associated with a trait of interest what should it have?
- have a measurable (observable) effect on a trait of interest
What effect do most genes have on a trait?
- most genes have genes have small effects on a trait (few percentage)
How can changes in DNA sequence be measured?
- sequencing
- PCR
- SNP chip
What does SNP stand for?
- single nucleotide polymorphisms
What are VNTRs?
- variable number tandem repeat sequences
What are types of VNTR’s?
- microsatellite - used in paternity tests
- minisatellite
= these typically have very little effect on performance
Describe the process of recombination?
- whilst chromosome pairs are aligned, the DNA strands can break and pas over each other, causing joining of a strand from one member of a pair to the other
What does recombination result in?
- results in transfer (usually in both directions- reciprocal) of a bit of one chromosome copy to another
- this can carry genetic variants
What leads to an increased chance of a recombination event?
- the further apart the two regions are on the chromosome
What is a haplotype?
- genetic variants that occur on the same chromosome strand are called a haplotype
To detect if markers are linked what should be distinguish between?
- distinguish between maternal and paternal alleles of a genetic marker
Markers must be what in at least one of the two parents of the mapping population?
- polymorphic
What would you do to work out if the is independent assortment (no linkage)?
- count the number of offspring to different genotypes and comparing to the frequency of segregates assuming independent assortment (chi sqaure)
What would a recombination frequency between two markers of 50% indicate?
- independent assortment - no linkage
Once you have the recombination frequencies between each pair of genetic markers, you can work out what?
- which markers lie closest to each other (lowest recombination frequency)
- do this for all markers
The distances of markers are not true physical base pair sizes but a measure of RF called what?
- centimorgans
We can map physical traits provided there is what?
- a genetic basis for them
physical traits have to be measurable quantitively what does this mean?
- there is measurable variation across a range
Due to these traits being able to be measured quantitively what does this mean the genetic map positions we obtain are called?
- called quantitative trait loci (QTL)
