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319 Breeding Systems

319 Breeding Systems - BREEDING/MATING SYSTEMS TWO GENERAL...

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BREEDING/MATING SYSTEMS TWO GENERAL TYPES OF BREEDERS: 1. Seedstock Breeder: The primary goal of the seedstock breeder is to improve the genetic makeup of his population. He wants to produce a population that is superior in an economic trait(s) due to increased homozygosity of gene pairs and gene combinations. This population will consistently and uniformly produce superior individuals that will also produce superior offspring. The seedstock producer markets GENETIC SUPERIORITY. 2. Market Breeder: The primary goal of the market breeder is to improve the performance of his population. He wants to produce a population that that excels in performance. He is NOT concerned with uniformity or consistency, but is concerned with maximum performance in an environment . He is not concerned with future generations since he will market all offspring. Market breeders try and maximize gene combinations that result in superior performance of the INDIVIDUAL. This is usually attained by increasing heterozygosity of the individual. Heterozygous individuals DO NOT breed true. The market breeder markets a SUPERIOR INDIVIDUAL. Principles of Inbreeding: The production of offspring by parents more closely related than the average of the population. The closer the relationship between the parents, the more the offspring will be inbred. Kinds of relatives mated % of inbreeding in offspring* Full brother to full sister 25.0 Half brother to half sister 12.5 First Cousins 6.3 Double first cousins 12.5 Uncle to niece/Aunt to nephew 12.5 Grandparent to grandchild 12.5 Assumes that the parents themselves are not inbred. * The % of inbreeding is an estimate of the increased homozygosity of genes in the offspring compared to their non-inbred parents.
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Most livestock producers are familiar with inbreeding and most avoid it as much as possible. Any familial problems will be MAGNIFIED by inbreeding: Increase in genetic defects, Decline in vigor and hardiness, and Decline in performance due to decline in vigor. However, with proper selection, father-daughter matings have been proven to result in superior offspring. When one looks to the establishment of BREEDS, especially under natural selection, the incidence of inbreeding was quite high. This led to the establishment of the specific traits associated with that specific breed. Inbreeding increased the homozygosity of the population and the result was the development of a consistent, uniform family that is genetically engineered to succeed in a specific environment. Any individuals that did NOT possess the superior traits, or expressed genetic defects were culled by nature. This significantly reduced the frequency of detrimental genes and gene combinations in the population. GENETIC EFFECTS OF INBREEDING: Inbreeding makes more pairs of genes in the population homozygous regardless of the type of gene action involved.
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