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Genetics in Agricultural Breeding Programs Natural Selection • Mechanism for evolution in natural populations • Organisms with best traits suited to the environmental factors affecting a population are most likely to survive and reproduce. – Results in the inheritance of the same well-suited traits • Important traits in natural selection-disease resistance, size, color pattern/camouflage, etc. Natural Selection • Types of Natural Selection – Stabilizing selection – Directional selection – Disruptive selection Stabilizing Selection • Individuals with the average or norm for a trait have an advantage over other forms of the trait – Example: gray moths (norm) are favored over black and white moths Directional Selection • Individuals with one extreme or less common version of a trait are favored over other forms of the trait. – Example: Black moths are favored over gray or white moths Disruptive Selection • Multiple extremes or alternative forms of a trait are favored over the norm – Example: Black moths and white moths are favored over gray moths Selective Breeding • Method of breeding plants and animals utilized in agriscience to produce offspring that possess certain characteristics desirable to agriculturists – Utilized for generations-produced the first domestic animals in early civilizations Selective Breeding • Used to select for a variety of traits including: – – – – – – – Muscling/Size Fat content Breeding Capability Color Speed/Agility Temperament Milk Production Selective Breeding • Methods for selective breeding: – – – – – Artificial insemination Pen/field breeding Isolation Breeding-inbreeding Mechanical pollination of plants Hybridization of plants and animals Selective Breeding • Selective breeding is accomplished much quicker in plants than animals due to growth rates and ease of propagation/production Selective Breeding Techniques Objective: Summarize the pro and purpose of selective bree techniques Techniques in Animals • Progeny testing is used to determine the value of male livestock by analyzing the transmission of traits to offspring and its breeding potential • Artificial insemination has proven to have the greatest impact on animal breeding since the first domestication of livestock. Artificial Insemination • Semen is collected from male individuals – methods vary widely by the type of animal – Artificial vaginas are used for larger mammals. • Semen is checked for viability and flash frozen in specialized straws. – Straws should be placed in storage tanks filled with liquid nitrogen, till use. – Semen stored under proper conditions has proven viable decades later (-320ºF) – Female is treated with prostaglandin (hormone) to induce estrus or heat – Semen straws are immediately thawed in water (99ºF) and soon after inserted into the mother using a specialized release gun. Sperm Sexing • Utilizes a cytometer cell sorter to separate male sperm from female sperm – Sperm with X chromosomes (female sperm) weigh more (contain more DNA) than those with a Y and can thus be dyed and separated because they absorb more dye Invitro-Fertilization • Method of removing eggs from a mother for fertilization under laboratory conditions. – A large number of eggs are collected from the ovaries of an outstanding female and fertilized in Petri dishes under laboratory conditions – Embryos can be inserted into surrogate mothers or frozen for later use – Offers the most control and requires the least amount of semen. Birth Through Surrogate Mothers • Hormones are used to cause the female to superovulate (produce a large number of eggs). • Original mother undergoes artificial insemination • Fertilized eggs are removed by a process called FLUSHING to be placed in other female animals for development. Cross-Pollination in Plants • Method used to select particular parents for the production of seed in plants. • Process – Plants possessing desirable characteristics are selected and carefully monitored – Pollen can be gathered from male plants (or flowers) months or in some cases, years in advance and refrigerated for storage – Flowers on the female part must be covered prior to opening, and if capable of self-pollination, must have the stamens removed. – Once the female flowers open, pollen from the male should be placed on the stigma, and the flower covered again. • Record keeping is critical in crossing plants. Selecting Plants and Animals for Breeding Observe Patterns of Heredity • The occurrence of genetic disorders in offspring or parents is an indicator that the parent may have a recessive gene for the disorder • Though genetic recombination is random, some animals are more likely to transmit genes than others • Keeping careful breeding records improves effectiveness Select Animals Carefully • Along with a good genetic background, animals used in selective breeding should be: – Healthy-old injuries or illnesses are not a factor unless they are a result of genetic propensities or impair breeding capabilities – Carefully monitored-nutrition levels, pests and stress can all reduce breeding viability. Some very good specimens are completely isolated. Select Animals Carefully • Hybrids should be avoided, since traits expressed in the organism are rarely transmitted to offspring – The process of inbreeding isolates genes for only a single generation, as many are recessive. Carefully Plan Breeding Crosses • Plants can be crossed not only within species (interspecific), but also within genus (intergeneric), and even, in rate cases family (interfamilial) • Animals are usually limited to crosses within the same species Methods for Producing Selective Breeding Programs Inbreeding • Crossing organisms that are genetically related – Crossing two plants to produce an f1 generation, then crossing two of the f1 offspring to create an f2 generation Backcrossing • Crossing offspring from a cross with one of the previous parents, or a similar organism, to maximize the expression of certain traits. – Often used after intergeneric crosses to produce offspring that possess more characteristics from one genus.