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Genetics > Outbreeding > Flashcards

Outbreeding Flashcards

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1
Q

What is outbreeding?

A

mating of individuals less closely related genetically than the average of the population

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2
Q

Where is outbreeding extensively used?

A

meat and animal production

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3
Q

What are the 4 types of outbreeding?

A

within breed, grading up, crossbreeding, and species crossing

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4
Q

What is Within Breed outbreeding?

A

crossing inbred lines

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5
Q

What is Within Breed outbreeding often used for?

A

poultry

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6
Q

How does Within Breed outbreeding occur in poultry?

A
  • there are several strains/lines of one breed
  • within each line there is intense selection for economically important traits
  • over time they become genetically distinct
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7
Q

What is Grading Up also called?

A

topcrossing

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8
Q

What is Grading Up outbreeding?

A

mating purebred males (that are superior) to non-purebred females (grade)

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9
Q

What is Grading Up outbreeding attempting to do?

A

create a purebred population

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10
Q

What is Crossbreeding outbreeding?

A

crossing different breeds

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11
Q

What is Species Crossing outbreeding?

A

crossing closely related species

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12
Q

What are examples of Species Crossing?

A

Horse x Donkey, Cattle x Bison, Bos Taurus x Bos Indicus, Angus x Brahman

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13
Q

Why are angus and brahman bred together?

A

combines growth rate, carcass attributes of Angus w/ hardiness and adaptability to hot humid conditions of Brahman

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14
Q

Who first bred angus and brahman?

A

USDA in coastal Louisiana

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15
Q

What does outbreeding do genetically?

A

increase heterozygosity

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16
Q

How does outbreeding affect deleterious recessives?

A

keeps them in heterozygous form, so they are not expressed (masked)

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17
Q

Does outbreeding eliminate deleterious recessive alleles?

A

no, it perpetuates them by masking their expression

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18
Q

How does outbreeding do phenotypically?

A

heterosis or hybrid vigor

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19
Q

What is heterosis?

A

the degree of superiority of the outbred offspring for a particular trait as compared to the average of the parental line or breed

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20
Q

What is observed heterosis the net effect of?

A

such influences at all loci affecting the trait

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21
Q

What is heterosis the difference between?

A

the average of all crossbreds, in comparison to the average of all purebreds

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22
Q

How do you calculate heterosis?

A

mean of F1 offspring - mean of parent breeds

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23
Q

How do you calculate percent heterosis?

A

(mean of F1 offspring - mean of parent breeds) / mean of parent breeds x100

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24
Q

Why isn’t crossbreeding used for dairy cattle?

A

No breed, when crossed with Holstein, will produce a F1 generation crossbred cow whose fluid milk yield exceeds that of straightbred Holstein

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25
Q

Does crossbreeding always improve the efficiency of production?

A

no

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26
Q

How is crossbreeding used for meat production?

A

crossbreds often don’t exceed the better purebred parent for individual traits such as survival, growth rate feed efficiency, and carcass merit, BUT heterosis for all the traits contributing to overall population efficiency will result in a greater net economic merit

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27
Q

What is breed complementation?

A

combining the desirable characteristic (traits) of 2 or more breeds (or lines)

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28
Q

What is an example of where breed complementation is used?

A

commercial beef cattle producers

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29
Q

What are angus characteristics?

A

moderate mature size, good fertility, milk production higher than Hereford, muscle is more marbled after a standard time on feed

30
Q

What is necessary for carcass to grade choice under USDA?

A

marbling/intramuscular fat

31
Q

What does the degree of heterosis and complementarity depend on?

A
  • genetic relationship of parents

- heritability and ability to measure trait

32
Q

How closely related should parents be to increase heterosis?

A

more diverse they are the more chance of heterosis

33
Q

What kind of relationship do heterosis and heritability have?

A

inverse

34
Q

What specific industries use outbreeding?

A
  • commercial cow/calf
  • swine
  • poultry (meat breeds)
  • sheep (meat breeds)
35
Q

What is the goal of commercial cow/calf?

A

produce 1 calf a year

36
Q

Why is outbreeding used in commercial cow/calf?

A

take advantage of heterosis because fertility is a lowly heritable trait

37
Q

Why are swine outbred?

A

maximize reproduction and growth (maternal lines)

38
Q

How are swine outbred?

A

extensive crossing of inbred lines (reciprocal recurrent selection?)

39
Q

What is reciprocal recurrent selection?

A

system of selection for increasing the combining ability of two (or more) lines (or breeds) that have demonstrated from past crosses that they develop well

40
Q

What are the two types of reciprocal reccurent selection?

A
  • general combining ability (GCA)

- specific combining ability (SCA)

41
Q

What is general combining ability?

A

evaluating how one breed will combine with several other breeds in a series of crossing (cross one as male and then reverse and use other as male and then evaluate that too)

42
Q

What is specific combining ability?

A

evaluating how two breeds will combine

43
Q

How does reciprocal recurrent selection develop superior inbred lines?

A

crossing more genetically diverse lines of two breeds=superior stock

44
Q

What is the net result of Reciprocal Recurrent Selection?

A
  • development of genetically diverse inbred lines
  • better performing crossed lines would express greater heterosis
  • those inbred lines could then be crossed with inbred lines of other breeds to generate more heterosis
45
Q

Why are meat poultry breeds outbred?

A

growth advantages

46
Q

How are dairy cattle bred?

A

outcrossed within breed but rarely between breeds

47
Q

Why are dairy cattle rarely bred (not about a specific breed)?

A

economics-established very specific parameters for value of product

48
Q

What is days open?

A

a reproductive trait measured in dairy, meaning days not pregnant

49
Q

What is desirable days open?

A

60-90 days, don’t want to exceed 90

50
Q

Is days open an inheritable trait?

A

yes

51
Q

What does hybrid vigor increase?

A

fertility and health/survivability

52
Q

What does dairy(?) crossbreeding result in?

A

hybrid vigor, reduce inbreeding, breed complementation

53
Q

In what livestock is limited crossbreeding used in?

A
  • dairy cattle
  • poultry (laying hens)
  • wool sheep
54
Q

What kind of breeding is used for laying hens?

A

extensive line crossing

55
Q

Why are laying hens not crossbred?

A

crossing a layer and broiler won’t meat either objective, it is not sustainable

56
Q

Why are wool sheep not crossbred?

A

little response to heterosis, heritability of most wool traits is moderate to high (when heritability is high, heterosis is low)

57
Q

When is crossbreeding best in terms of heritability?

A

when heritability is low

58
Q

How is heritability represented?

A

h^2

59
Q

What things must be considered before you attempt systems of Crossbreeding?

A
  • Define objectives
  • Breeds
  • Herd size
  • Implementation cost versus Expected Return
  • Nothing is Free
60
Q

How are objectives defined?

A
  • traits of interest (level of heterosis)

- complementarity achievable

61
Q

What must be met in terms of Breeds for crossbreeding to occur?

A
  • compatibility of breeds using GCA test
  • availability of quality animals (want to be superior)
  • continued supply
62
Q

What does continued supply mean?

A

source for replacements

63
Q

What herd size is wanted for crossbreeding?

A

the larger the better, but is more complex because need more land, tags, etc

64
Q

What is implementation of cost versus expected return?

A

would the return justify all the effort

65
Q

What is the significance of nothing being free?

A

increased performance will require greater availability of feed and nutrients

66
Q

What are maternal swine breeds?

A

larger litter size, produce more milk, better mothering ability

67
Q

What are paternal swine breeds?

A

faster growth, better meat

68
Q

What are examples of maternal swine breeds?

A

Yorkshire, Landrace, and Chester White

69
Q

What are examples of paternal swine breeds?

A

Duroc, Hampshire, and Spots

70
Q

What is a reciprocal cross?

A

test the reverse sex of the direct cross. If direct cross is a male Angus x female Hereford, reciprocal cross is female Angus x male Hereford

71
Q

Does the performance of reciprocal crosses make any diffference?

A

yes

Genetics (24 decks)

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