Principles of Selection Flashcards
is the art and science of the genetic improvement of farm animals.
Animal Breeding
choosing some animals as parents of the next generation of animals.
Selection
removal of inferior animals
Culling
What is the basis of animal breeding is ?
correct selection of breeding animals for mating
obtained as a regression of a phenotypic deviation
Estimation of Breeding Value
records deviated from a mean
Phenotypic Deviation
Breeding Value in the phenotypic deviations
Regression
is the proportion of the phenotypic variance that is due to genetic effects including additive, dominance and epistasis:
Heritability in the broad sense (H2)
is the proportion of the phenotypic variance that is due to additive genetic effects only.
Heritability in the Narrow Sense (h2)
What does the heritability in the narrow sense measure?
It measures the degree to which the offspring —-
If a trait has a large heritability, animals with high performance for the trait will produce offspring with —- ———
resemble their parents in performance for a trait.
High Performance
If a trait has a small heritability, performance records of parents reveal —— —— about the performance of their offspring
Traits with low heritability ranges from??
h2 < 0.20
Moderately heritable traits ranges from ??
h2 0.2 to 0.4
Highly heritable traits ranges from?
h2 > 0.40
Traits with low heritability (h2 < 0.20): charactersitics:
• reproductive traits
• longevity or productive live ( about 0.10)
Moderately heritable traits (h2 of 0.2 to 0.4): Characteristics: ll
• Milk yield, fat yield and protein yield (0.25-0.35)
• Birth weight
• Weaning weight
• Yearling weight
Highly heritable traits (h2> 0.4):
Characteristics:
• Carcass traits and traits related to skeletal dimensions like mature body weight
• Fat and protein% in milk.
animals are selected based on their ancestors, where the performance of these ancestors is known then a useful selection can often be made.
Pedigree Selection
the breeding value of each individual is assessed on the average performance of a random sample of its progeny, and animals are selected or culled based on this progeny performance
Progeny Testing
any animals unsatisfactorily for the character being selectedcan be culled before breeding is commenced.
Mass or Individual Selection
selection based on theperformance of nearby relatives
Family Selection
selection is made for one trait or character at a timeuntil it is improved, then for a second trait and so on.
Tandem Selection
a method where minimum standards of performanceare established for each trait in the criteria. Anyanimal not satisfying the minimum standard for alltraits is culled.
Independent Culling Level
Each character is given a score and scores for all characters being considered are added together. Those with the poorest total scores would be culled.
Selection Index
breeding of two or more different breed of animal.
Crossbreeding
means that breeding of animal with the same breed.
Purebreeding
Mating between animals, which are more closely related to each other than the average relationship between all individuals in the population.
Inbreeding
1st mating: A x B
1st generation: ½ A ½ B
2nd mating A x ½ A ½ B
2nd generation ¾ A ¼ B
Inbreeding
Mild form of inbreeding. Mating of cousins, grandparent to grand offspring or half-brother to half sister.
Linebreeding
Example: A is ♀; B & C is ♂
1st mating: A x B A x C
1st generation: ½ A ½ B ½ A ½ C
2nd mating ½ A ½ B x ½ A ½ C
2nd generation ½ A ¼ B ¼ C
Linebreeding
Mating of animals of different families within the same breed that are not closely related. (For at least the first four to six generation.
Outcrossing
is the mating of two animals from different breeds.
Crossbreeding
The increased level of performance of the offspring as to compare to the average of the parental type is known as
Heterosis or Hybrid Vigor
There is a ——– relationship between heterosis and heritability:
the traits that demonstrate the most hybrid vigor are those that show the ——- heritability.
Reciprocal
Lowest heritability
Crossbreeding can be used to:
•Develop new breeds
•Upgrade local breeds
Two different populations can be crossed with each other to produce an F1 generation which is used only for production purposes and not for breeding.
Single Two-Way Cross
This system relies on the crossing of two breeds A and B to produce a female excelling in maternal performance in a particular environment and the use of a third breed to produced the ideal animal for the market product.
Three Way Cross
Populations A and B are first crossedwith each other, and so are C and D to obtain the F1generation A x B and C x D. These are then crossedtogether to produce the double hybrids AB x CD. It isnecessary to maintain only relatively small number ofanimals of the lines A, B, C, and D.
Four way cross
The F1 females are back crossed to oneof the parental populations. For example, A x B females are mated with A or B to produce an offspring AB x A or AB x B.
Backcross
This method takes fulladvantage of heterosis in the F1 females and half ofthe potential heterosis in the offspring.
Backcross
In which males of each of the two breeds involved are used alternately; this system hasthe advantages over the two-way cross, in that thecrossbreed females can be used for breeding.
Two-way rotational cross
A x B —— AB
First mating : A x AB
Second mating: B x AB
Third mating: A x AB
Two-way rotational cross
In which males of each of the three breeds are used in turn; cross bred females produced can be used for breeding.
Three-way rotational cross
A x B x C ——- ABC
First mating : A x ABC
Second mating: B x ABC
Third mating: C x ABC
Three way rotational cross
Selection for Quantitative Traits
Estimate merit (BV’s)
Determine accuracy of estimation
Predict response to selection
Methods of Selection
Tandem Selection
Independent Culling Level
Selection Index
Aids to Selection
Pedigree Selection
Progeny testing
Mass or Individual Selection
Family Selection
Mating Systems
Cross breeding and Purebreeding
Types of Crossbreeding
Inbreeding
Linebreeding
Outcrossing
Methods of Crossbreedings
Single two way Crosses
Three way cross
Four way cross
Back cross
Two way rotational cross
Three way rotational cross
