For thousands and thousands of years, about 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 those genes or traits to display in extreme ways to increase the yield, efficiency or anything else that makes the crop or animal more beneficial on the farm. 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 selectively bred for around ten thousand five hundred years. By choosing cows that were the largest or produced the most milk to have offspring, we unconsciously increased the efficiency with which they made milk, changed their biology to fit more meat in them, and domesticated them. 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 have had broader impacts on the environment and ecosystem. Say no to plagiarism. Get a tailor-made essay on 'Why violent video games should not be banned'?Get the original essaySelective breeding cows originated from farmers capturing and breeding a species known as the Auroch - which has since become extinct almost 400 years old - and probably the first time they were used for meat rather than their milk. For this reason, it is likely that only the quietest ones are truly cultivable and tame, since these are the ones who actually had the offspring, passing on the more domesticated genes that made it easier for farmers to work and breed them, passing on thus most often the genes of the calmest. This means that only those best suited to the environment in which they were raised or to the intended purpose of the producers when selecting them were able to pass on their genes, meaning that the next generation's gene pool will have in as such a higher frequency of these preferred genes and make farming easier and more efficient over time. This system is by no means perfect, as breeding a cow that has a few genes that you find favorable will still pass on those genes due to the randomness of the meiosis process as well as the risk of mutation and gene presence hidden. Although the traits he exhibits (his phenotype) may be favorable, his genes (genotype) may not be favorable. For example, if the parent with the favorable genotype was heterozygous with an unfavorable recessive gene and is mated with another individual also heterozygous with this unfavorable gene, there is a good chance that their offspring will be homozygous for this recessive gene, this is i.e. the phenotype. what you wanted from the original animal is not expressed. Examples in cows include genetic diseases like dwarfism or crooked tail syndrome, but in reality this process applies to any small inconvenience, like maybe they don't breed as well or produce not as much nutritious milk. Over time, breeding for selected traits has become much easier to make the traits you want on purpose, as people have discovered ways to discover an animal's genotype. With this knowledge, dairy and beef farmers can breed two individuals with one gene, either homozygous dominant or homozygous recessive, toensure 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, you cross an organism that expresses a trait with an organism that you know is heterozygous and by looking at the resulting offspring you can determine whether the first parent is dominant or heterozygous for the trait you want. Other newer methods include marker-assisted selection or "MAS", which is used to mark a specific gene, usually difficult to measure/observe, transmitted very rarely (recessives) or are not expressed until later in life , in order to indirectly select a genetic determinant of a trait of interest. The reason MAS is a newer breeding technique is because very few traits in general have markers and it was first observed naturally - allegedly - 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 marker in beans » Quote source. Steps to effectively using MAS include mapping the gene into the question location or "quantitative trait locus" (aka QTL) using various methods, then using this information for marker-assisted selection, and genes linked or very close in the animal's DNA are used to mark the presence of the desired traits. It is always possible for a crossover to occur between these two related 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 domesticating the cow, its genetic diversity has diminished as we select for all the genes we don't want or need from the species over time as sub -product. Another biological implication is that, for the same reasons MAS works, reproducing a gene can be very difficult or impossible due to related or very close genes. Linked genes are those found very close to each other on the same chromosome and have a recombination frequency of less than 50%, an example of this in cows could be milk and fat production. A farmer can select for a cow that is tall, muscular, or produces a lot of milk, but those genes could also have negative side effects, such as fertility or immune system problems, that would likely outweigh the benefits of selection. for this gene. This is because they would either all die from the same disease due to their lack of variation, which could negatively or positively affect the ecosystem in significant ways if all the cows were suddenly wiped out. Cloning is also a newer technique that would allow the selection of specific individuals in order to preserve a specific genotype that the farmer finds very effective or practical without having to go through the risk/reward system of their normal reproduction and would thus have a higher success rate because the scientists involved are in complete control of the process. Additionally, it is quite easy to add additional genes to a species or individual that they do not naturally possess, for example cows that can donate their plasma to humans. This technique is called transgenesis, where the genes of one species are placed into the genome of another species or through the use of gene editing by.