ANSI 3433 Lecture Notes - Lecture 4: Selective Breeding, Zygosity, Heterosis
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How Are Animal Populations Improved?
Purpose of Animal Breeding is to improve populations.
Two Basic Tools of Animal Breeding (Decisions):
- Selection – process that determines which individuals become parents, how
many offspring they produce and how long they remain in the breeding
population
- Mating – determining which males will be mated to which females
Mating is distinctly different than selection
In selection we are picking a group to become parents; in mating, you match males to females
from the selected group.
Dam – female parent
Sire – male parent
Selection
- Results in long-term change
- two types:
o natural– great evolutionary force fueling genetic change in all living things.
Affects wild and domesticated animals; for example, all animals with lethal
genes are naturally selected against
o artificial – under human control, the type of primary interest to animal
breeders
We focus on artificial selection, but cannot ignore natural selection.
Artificial selection has two aspects:
- Replacement selection – deciding which animals will become parents for the
first time. (replacing the culls) – not just young aials, exaple……a AI sire.
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Artificial Insemination (AI) – a reproductive technology in which semen is collected from males,
then used in fresh or frozen form to breed females.
- Culling – determining which animals will no longer remain parents.
Both determine which animals reproduce, and which do not.
Goal of animal breeding is to:
- let individual with the est gees reprodue, so that the…
- next generation has on average better genes
- over time, frequency of desired genes in the population will increase
Animals with the best genes are the ones with the best Breeding Value. Breeding Value is the
genetic value of an individual as a parent
Phenotypic Selection
- simplest form of selection
- ignores pedigree, performance of relatives. Only info used is the individual
performance of each animal being considered for selection.
- underlying assumption is that those with best phenotype have best genotype
(breeding value) Problem?
Environment cant be evaluated just by looking at the animal. The
environment plays a large role!
Measuring Performance
Selection requires performance testing
- Varies among species
- Recording phenotypes for traits within contemporary groups
- Systematic measurements of performance (phenotype) in a population
- Primarily done in purebred seedstock programs
Contemporaty group – a set of animals that are same sex, managed alike, close to the same age
and given the same opportunity to perform in the same environment. (submitting individual
performance measures on animals for genetic prediction requires proper contemporary
grouping)
- Use additional information to increase accuracy of selection, such as
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