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REPRO > Animal breeding > Flashcards

Animal breeding Flashcards

1
Q

What are the drivers for animal breeding?

A
  • Demand for low cost, high quality food
  • Competition
  • Consumer demands
  • Appearance or other traits
  • Removal of undesired/negative traits
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2
Q

What are the benefits of using genetics for animal improvement?

A
  • Improvements easy to perpetuate
  • Assist in meeting market requirements
  • Improve overall productivity and profitability
  • Improve specific traits e.g. growth rate, carcasse yield, fleece weight, fibre diameter etc
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3
Q

List sources of genetic variation

A
  • Mutations
  • Gene flow
  • Sex
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4
Q

Describe mutations as a source of genetic variation

A
  • Changes in DNA
  • Single mutation can have large effect
  • Can be beneficial, neutral, harmful
  • random
  • Germ-line mutations important in breeding
  • No effect, small effect or important effect
  • Mistake in copying or faulty repair after environmental damage
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5
Q

Describe gene flow as a source of genetic variation

A
  • Any movements of genes from one population to another
  • Differences in populations of same species, bringing together adds to genetic variation
  • Within a population can introduce/reintroduce genes
  • Across populations, can make distant populations more genetically similar to one another = reducing change of speciation
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6
Q

Describe sex as a source of genetic variation

A
  • Can introduce new gene combinations into a population
  • Genetic shuffling important for genetic variation
  • Sex organs are where genetic information is exchanged or manipukated
  • In females, happen before birth while oocyte produced
  • Crossing over, independent reassortment
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7
Q

Define qualitative traits

A
  • Characterised by segregation in classical mendelian ratios, purely genetic
  • .e.g coat colour, absence of horns
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8
Q

Define quantitative traits

A
  • Traits that can be marked on a scale
  • E.g. growth rate, milk yield
  • Often polygenic, usually multiple genetic loci
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9
Q

Give exceptions to the standard definition of quantitative traits

A
  • single polymorphic locus with multiple, differentially expressed alleles can give rise to continuous variation within natural population
  • Expression of a quantitative trait controlled by a mutant allele at a single locus with high degree of variable expressivity
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10
Q

What affects phenotype?

A
  • Genetics and environment
  • Is the observed category or measurable level of performance for a trait in an individual
  • Environmental can affect animal performance
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11
Q

List environmental factors that can affect phenotype

A
  • Temperature
  • Light-dark
  • Shelter, housing
  • Bedding
  • Medication
  • Hydration
  • Nutrition
  • Maternal care
  • Intrauterine conditions
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12
Q

What is meant by epigenetics

A
  • Heritable changes in gene expressions that are not caused by changes in DNA sequence
  • Hence identical twins can express genes at different levels so can be told apart more earily as get older
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13
Q

What is the genotype frequence?

A

The proportion of animals within a herd/flock/breed that has each genotype. Are expresed as fraction of 1 whole i.e. 100 short horn cows 30 red, 50 roan, 20 white = 0.3 RR, RW = 0.5, WW= 0.2

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14
Q

What is gene frequency?

A

Where the genotype is weighted against the genotype frequency

  • i.e. are counting the number of alleles within a population
    i. e. if mating cows in a herd with RR bull, calculate the percentages of possible genotype outcomes (RR, RW, WW). Then multiply this for each genotype outcome, by the proportion of the herd made up by the cows of that genotype. Add up the results for the offspring genotype frequency for RR, RW and WW (which will be 0). To get gene frequency do (1xRR genotype frequency) + (0.5x RW genotype frequency) (since RW only half is R allele)
  • Only 2 alleles involved in this so 1-R frequency will give W frequency
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15
Q

What is the Hardy-Weinberg law?

A

Genotype frequencies in offspring depend solely on gene frequencies in parents

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16
Q

Outline pressures when making a decision about animal breeding

A
  • Availability of information
  • Financial and physical resources
  • Current breeds in use
  • Local traditions
  • Market demand
  • Personal preferences
  • Environment
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17
Q

Describe a breeding pyramid

A
  • Elite at top
  • Next/middle layer are multiplier
  • Bottom are commercial flocks or herds
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18
Q

Describe the elite breeders in a breeding pyramid

A
  • Breeding stock/nucleus breeders
  • Very few, careful genetic examination
  • Is where genetic improvement occurs in response to feedback from commercial/multiplier layers
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19
Q

Describe the multipliers in a breeding pyramid

A
  • Purebred/cross bred breeders
  • Multiplication is aim (plus specific testing of different crosses)
  • Sold on for production of commercial flocks
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20
Q

Describe the commercial flocks/herds in a breeding pyramid

A
  • End users
  • Marketing meat, milk or fibre
  • Not sold on for breeding
  • Give information on performance of genetic line back to multiplier and elite layers for genetic improvement
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21
Q

Describe rotational crossing within a herd

A
  • Males bred to a herd
  • Then rotate i.e. different male next service
  • Repacement females from original cross
  • Will be no inbreeding as new male used every time
22
Q

Describe terminal crossing

A
  • F1 mated with different breed to produce market animals

- No feedback to top layers

23
Q

Define crossbreeding

A
  • Selection of particular breeds to reproduce from in order to gain particular characteristics
24
Q

What are the advantages of crossbreeding?

A
  • Dramatic and rapid change where there are large genetic differences
  • Production of better genetic line e.g. Meidam pigs
25
Q

What are the disadvantages of crossbreeding?

A

Once done, difficult to remove unwanted characteristics

26
Q

Describe backcrossing

A
  • Used for breeding out a particular characteristic
  • E.g dogs with known problem bred with dogs breed without problem
  • Then cross subsequent generations repeatedly with the affected breed
  • End up with breed that looks similar to original but without problem
27
Q

Define heterosis

A
  • Hybrid vigour

- Extra performance above the mid-parent mean

28
Q

How does heterosis occur?

A
  • Crosses are used to breed in or out an observed characteristics
  • Many unobserved characteristics also benefit
  • Hybrid will do better
29
Q

Describe inbreeding

A
  • Breeding related animals
  • Natural occurenes
  • Some benefits
  • But also inbreeding depression - terminal lack of vigor and probably extinction
  • Gene pool contracts, fertility decreases, abnormalities increase and mortality rates rise
30
Q

Define response to selection

A

The change in mean performance of a population of animals as a result of selection (usually per year or generation)

31
Q

Explain how to quantify response to selection

A

Response to selection = selection differential x heritability

32
Q

Explain how to quantify response to selection per year

A

The response to selection over the generation interval (years

33
Q

Define generation interval (L)

A

The average age of an animal when their offspring are born

34
Q

List different schemes used to integrate information from relatives

A
  • Pedigree selection
  • Performance test
  • Sib-pair test
  • Progeny test
35
Q

Describe how pedigree index can be used to integrate information from relatives

A

Is an index combining information on ancestor’s performance

36
Q

Descibe the sib-pair test as a scheme to integrate information from relatives

A
  • Selection programme based on information from siblings

- Whateber is exhibited by that animal’s sibling will also be shared by teh animal to some degree

37
Q

Describe the progeny test as a scheme to integrate information from relatives

A

Based on performance of an animal’s offspring

38
Q

List considerations when choosing which animals to cull and which to use as replacements

A
  • Litter size
  • Recurring disease (e.g. mastitis)
  • Poor fertility
  • Parturition difficulties
  • Poor lactation and rearing ability
  • Poor maternal behaviour
  • Decreased productivity
  • Anoestrus
  • Abortion
  • Lameness
  • Disease
39
Q

Why is 40% the ideal proportion of a herd to replace each year in pigs?

A
  • Need to replace gilt after 6 litters, so this is around 40% of the herd each year (productivity starts to decline, more dystocia)
  • More replacement means more young gilts so more likely to get disease and overall productivity will decrease
40
Q

What are some practical applications of inbreeding?

A
  • Breeding of companion animals
  • Control of inheritable diseases
  • Management of zoo populations and endangered species
  • Estimation of heritability
  • Artificial selection programmes
41
Q

What are the disadvantages of inbreeding?

A
  • Results in animals with both favourable and unfavourable genes increased
  • Drives towards situation where very few if any of population are heteroxygous
  • Removes genetic variation (thus a populaiton may all be susceptible to the same disease etc)
42
Q

Define inbreeding depression?

A

The manifestation of poor gene combinations that significantly decrease performance due to combination of alleles with a negative effect on general fitness of a population

43
Q

Compare outbreeding and inbreeding

A
  • Outbred: breed 2 highly inbred but unrelated individuals together
  • Inbred: breed 2 related outbred individuals
44
Q

Explain how in half-sib mating, the offspring may have 2 copies of an ientical allele

A
  • Half-sib parents carry one gene from shared parent
  • May have the same allele of that gene
  • May pass on the identical allele producing offspring that is homozygous at that locus
  • Identical by descent
45
Q

What is the inbreeding coefficient?

A

The probability of inherting the same allele from 2 half-sib parents
- i.e. the porbablity that both alleles at a single locus are identical by descent

46
Q

How can the relationship between offspring to ancestor be calculated?

A
  • Half genes in common with parent, quater with grandparent and so on
  • the total number of generations separating relatives is n+n’ where n is the number of generations between ancestors and first relative, and n’ if the generations between ancestor and second relative
  • The relationship is (1/2)^(n+n’)
47
Q

List common methods used to reduce inbreeding

A
  • Deliberately choose less related individuals
  • Use more than one male from each elected full sib family
  • Use selected parents only once
  • Use factoral mating designs
48
Q

Outline the genetic concerns of breedig animals in captivity

A
  • Limited gene pool
  • Leads to inbreeding
  • Creates homozygous individuals
  • Higher mortality rate in inbred offspring
  • Likely that a new infection would kill entire population as all have same immunity etc
49
Q

Describe breeding strategies used to detect heterozygous carriers in dogs

A
  • Pretest potential breeding stock e.g. detection of PFK levels, where carrier will have levels between normal and affected dog
  • Clinical screening (detects homozygous) prior to breeding
  • DNA testing
50
Q

What are prerequisites for developing breeding programmes?

A
  • Identification of genotype of potential dams and sires
  • Develop programme that selects against mutant allele
  • Most genetic diseases in dog are autosomal recessive thus can be carriers, need to establish ways to prevent breeding from carriers

REPRO (30 decks)

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