For thousands and thousands of years, approximately 10,500, humans have selectively bred animals. This process works by selecting the most favorable member of a species and allowing it to reproduce, passing on its genes, which over time causes these genes or characteristics to display in extreme ways to increase production, efficiency, or something else that makes the most profitable crop or animal to raise. Of course, humans didn't realize this was what we were doing and only more recently discovered the biological mechanisms behind this effect, which we dubbed artificial selection. A fantastic example of this would be the dairy cow, an animal that we have been selectively breeding for about ten and a half thousand years, by choosing cows that were larger or that produced more milk to have offspring, we have unconsciously increased the efficiency with which they produce milk, they alter their biology to have more meat and domesticate it to tolerate or enjoy human contact, all for the sake of food production. Of course this has effects that go beyond just the dairy cow and has had wider impacts on the environment and ecosystem. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Selective breeding cows originated from farmers who caught and raised a species known as Auroch, which has been extinct for nearly 400 years, and probably the first at the time were used for meat rather than milk. For this reason it is likely that only the calmest ones were actually cultivable and tamable, as such were the ones who actually had offspring, passing on the tamer genes which made it easier for farmers to work with them and raise them thus passing on the genes of calmer ones more often. This means that only those best suited to the environment in which they were bred or the purpose intended by the breeder were able to pass on their genes, meaning that the next generation's gene pool will as such have a higher frequency of these preferred genes and make farming easier and more efficient as time goes on. This is by no means a perfect system, as breeding a cow that has some genes that you find favorable will always pass on those genes due to the randomness of the meiosis process and the possibility of hidden mutations and genes being present. While the traits he displays (his phenotype) may be favorable, his genes (the genotype) may not be. For example, if the parent with the favorable genotype was heterozygous with an unfavorable recessive gene and is crossed with another individual who is also heterozygous with that unfavorable gene, there is a real possibility that his offspring will be homozygous for that recessive gene, that is, the phenotype you wanted from the original animal is not expressed. Examples in cows include genetic diseases such as dwarfism or crooked tail syndrome, but in reality this process applies to any small inconvenience such as perhaps they don't reproduce well or don't produce as much nutritious milk. As time went on breeding for selected traits became much easier to purposely like desired traits as people discovered ways to discover an animal's genotype. With this knowledge, dairy and cattle breeders can breed two individuals who carry a gene, either homozygous dominant or homozygous recessive, to ensure that the offspring produced are “purebred” for that specific trait. The first way to find out the genotype of an animal used would be a test cross, that is, crossing an organism that expresses a trait with one that is knownbe heterozygous and by observing the resulting offspring you can determine whether the first parent is dominant or heterozygous for the trait you want. Other more recent methods include marker-assisted selection or “MAS”, used to mark a specific gene, usually difficult to measure/observe, very rarely passed on (recessive) or are not expressed until later in life, in order to select indirectly a genetic determinant of a cited trait of interest. The reason MAS is a newer technique in selective breeding because very few traits in general have markers and it was first observed naturally - supposedly - in 1923 by a man named Sax K. when he observed an “association of a simply inherited genetic marker with a quantitative trait in plants when he observed seed size segregation associated with segregation for a seed coat color indicator in beans” Source citation. Steps to effectively use MAS include mapping the gene to the question location or "quantitative trait locus" (also known as QTL) using various methods and then using this information for marker-assisted selection and the linked genes or very close together in animals' DNA are used to mark the presence of desired traits. It is still possible for crossover to occur between these two linked or very close genes, so two or more markers are usually used to indicate its presence and reduce the margin of error for homologous recombination. Since man began to domesticate the cow, its genetic diversity has decreased by breeding over time all the genes we didn't want or need out of the species as a byproduct. Another biological implication is that, for the same reasons that MAS works, reproducing a gene can be very difficult or impossible due to linked or very close genes. Linked genes are those that are located very close to each other on the same chromosome and have a recombination frequency of less than 50%, an example of this in cows would be milk and fat production. A breeder may select a cow that is large, muscular, or produces a lot of milk, but these genes could also have negative side effects such as fertility or immune system problems, which would likely outweigh the benefits of selecting for that gene. This is because they would all die from the same disease due to their lack of variation, which could negatively or positively affect the ecosystem in a big way if all the cows were suddenly wiped out. Cloning is also a newer technique that could allow for the selection of specific individuals in order to preserve a specific genotype that the farmer finds very efficient or convenient without having to go through the risk/reward system of breeding them normally and as such would have a rate more successful as are the scientists involved in complete control of the process. It is also quite easy to add extra genes to the species or individual that they may not possess naturally, for example cows that can donate their plasma to humans. This technique is called transgenesis, where genes from one species are inserted into the genome of another species, or the use of gene editing through various other means. The reason for these cows is the lack of blood donors to provide plasma to seriously injured patients, and since the farmer does not use the cow's blood for anything as it is, it is a kind of extra product that he can sell or give away. It works by inserting the gene responsible for producing plasma for humans and.