Ansc 1000, Week Five Notes
Ansc 1000, Week Five Notes ANSC 1000
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This 5 page Class Notes was uploaded by Olivia Schweikart on Saturday February 13, 2016. The Class Notes belongs to ANSC 1000 at Auburn University taught by Dr. Carolyn Huntington in Spring 2016. Since its upload, it has received 28 views. For similar materials see Introduction to Animal Sciences in Animal Science and Zoology at Auburn University.
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Date Created: 02/13/16
Genetics & Animal Breeding Week Five Notes Gene Interactions • Genetically, the phenotype can be altered by changing the environment o Example: if two identical twin bovine are separated and one is placed in a good environment while the other is in a lesser environment, they will not grow to the same standard (the one in the greater environment will much likely be larger in stature) • Linear interactions occur when genes interact with other genes along the same line of chromosome o Have not been seen in li vestock, focused more on animals such as fruit flies, etc. • Allelic interactions occur when genes interact with other genes along a homologous chromosome o While the genes may have the same loci, they address situations differently o Can sometimes be known as d ominance interactions due to the dominant gene being the gene expressed o Complete dominance § Example: If a BB is crossed with a bb, all offspring will be black due to the dominant B being present • Because of the allelic interactions this B will be expressed over the recessive allele o Lack of dominance § Considered a half-way point between the parents of the offspring • Example: If a sheep that is earless is crossed with one that has long ears, the resulting offspring may have short ears, meeting the two parents in the middle in terms of phenotype § Also known as additive gene action, due to each gene having its own phenotypic effect on the animal • Example: If animals with different daily gain rates are crossed, the resulting offspring may be in the middle of the two rates o Resulting offspring: § DD (0.2 lb./day) § Dd (0.15 lb./day) § Dd (0.10 lb./day) o Overdominance § This occurs when offspring have better characteristics than the parents, in other words, the heterozygous offspring outperform the homozygous parents • Heterosis- occurs when an animal tends to have better characteristics than the parents and outperform • Hybrid vigor- term for more productivity arising from crossbreds o In the beef industry, a lot of crossbreeding occurs, however in the dairy industry it is not a common occurrence o Partial dominance § The heterozygous offspring looks more similar to the homozygous dominant parents, however does exhibit some intermediate phenotypic expression § HYPP (hyperkalemic periodic paralysis) • Occurs when an animal has too much potass ium, which results in temporary paralysis • Epistatic interactions occur when genes interact with other genes along a non -homologous chromosome (another chromosome) o Will alter or mask the expression of another gene § Example: White coat color will mask other c oat colors (the WW results in albino horse which dies) • Can be lethal depending on genotype o Example: EEWW, EeWW, eeWW, (notice all contain the dominant form for the white coat —albino) are lethal o Those containing just the recessive form of the white coat are non-lethal to the animal (EeWw, and eeWw) § Example: EEww (black coat) § Eeww (black coat) § eeww (chestnut coat) o In horses, the extension gene is what determines the basic coat color § Example: EE and Ee result in black color expression, while ee results in ches tnut expression o The agouti gene determines coat color in foals § Example: AA and Aa result in bay color expression, while aa results in solid black coat expression • Black coat color in the horse industry is relatively uncommon • Bay coat color refers to the body being a chestnut color (or lighter) with black points on the body, be it the tail, legs, etc. • Temperature, along with many other environmental factors can affect the genetics of an animal o Example: Infertility due to excess heat o Example: Lack of light can alter breeding pattern Determining the Superior Animal • Can be difficult to identity a “best” breed • Animals perform better in different environments o Must be compared to its cotemporaries o If environmental differences exist between the animals, these differences cannot be selected for and then passed to the next generation § Example: Hog little size • Most are environmental causes • Litter size over a wide range of years has only increased slightly • Heritability of whatever trait is being taken into consideration is also a factor to take into consideration o How likely the genotype will be translated into the phenotype o Levels of heritability vary with different traits § Reproductive traits are lowly heritable § Growth traits are considered moderately heritable § Carcass size and weight is considered to be highly heritable • Traits with high heritability are going to respond better to selection o Will be more likely passed on to offspring, thus giving an animal that will most likely be selected for breeding • Correlated Responses are those that are related to other factors o Example: A bullock that weighs 75 pounds more than another bullock at the yearling weight will be considered to have weighed more at the time of birth Expected Progeny Differences • EPD (stands for expected progeny differences) o Based on some standard, this gives producers an idea of differences in animal performance § Looks at quantitative traits § Influenced by the individual’s own performance records, along with ancestors of that individuals and the animal’s contemporaries • The closer the ancestors are, the more influence their traits have in terms of pedigree o Can only be compared to other animals within the same breed o Able to give the producer an idea of which animals should be mated § Example of EPD • Weaning weight formula: Calf’s Genes – Intrinsic GrowWeaning ty – EPD o The difference recorded between animals using EPD is what is important § For example, if one sire’s EPD for birth weight was 1.5 and another sire’s was 6.0, the first sire would produce calves that have a lower birth weight than the second sire § This comparison still does not give a real number for birth weight, just an idea • The breed average for the birth weight EPD must then be taken into consideration o For example, if the first sire having a 1.5 EPD for birth weight is compared to a breed average of 2.6, we can take away that the sire will produce calves that are 1.1 lb. lighter than the breed average • Birth weights on animals do not want to be large due to dystocia being a problem for the mother after birth o Lighter weights lead to easier births for the mother o Instead of viewing close EPD values as “equal,” the term “accurate” is used § Range on a scale of 0 to 1, the latter being considered the most reliable/accurate • If lowly accurate (i.e. below 0.40), the data is unreliable • If from a low to medium range (i.e. 0.40-0.60), the data can be useful to take into consideration but should not be heavily relied on • If accurate on a medium to high range (i.e. 0.60-0.80) the data is trustworthy • If highly accurate (i.e. 0.80 or above) the data is highly reliable Continuous Variation in Traits • With any trait, a bell shaped curve can be attached • One set away from the midline is considered 1 SD (standard deviation) • Two sets away is 2 SD • Three sets away is 3 SD Quantitative vs. Qualitative • With quantitative traits, it does not matter who takes the measurement, the number will be the same due to it being objective o Measurement identical from person to person o Examples: F/G, various weights of animals, reproduction percentages o 100 + genes can be involved § Pleiotropy (for one specific trait, multiple genes can be involved) • Qualitative traits are very descriptive and can vary depending on the person that observes them o Example: Coat color o Typically, 1-4 genes involved Changing Animal Populations Genetically • For producers, it is desired that each generation should be better than the previous o Goal to improve population of herd rather than a select few • Unless environment is standardized, it can be hard to select animals for breeding o Could have good genes, but masked by surroundings o Weather, amount of food presence, etc. can all play a part in the difference between phenotypes due to environmental causes o Producers must adjust data for a variety of factors so environment can be standardized for the animals § Producers must take into account the age of the animal § Example: The standard weaning age for cattle is 205 days, however this may not be the case for all animals, therefore correction factors must be taken into consideration • Could be 195 days, 220 days, etc. • Example formula: (actual weaning weight – birth weight) (+birthweight + correctio factor (w aning age in days) • Sex must be taken into account, males weigh more than females • Placing animals in a contemporary group refers to placing them in a standardized environment with like animals o Placed in a group because of some common feature among them • Once placed in a contemporary group, producers are then able to see which animals perform better phenotypically • Ratios between animals in contemporary groups: Single animal’s measurement (x100) Average of Contemporary Group • Allows to see how the animal in a standardized environment performs relative to the rest of its group Selection • Certain animals are chosen for reproduction while others are not able to pass on their traits and reproduce • Can change the gene pool, as well as the frequency of reoccurrence for different genes • Genetic improvement depends on four factors o How much genetic variation is available for the population o How accurate is the heritability o How long it takes for new generations o How much pressure is placed on the herd in terms of changing the situation § Example: How many females bred to one bull
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