The selective breeding of animals has been practiced by humans for over 10,000 years. This involves choosing the best members of a particular species to breed with, then passing their genes onto the next generation. Over time, these genes or features can be used to improve the yield, efficiency, or any other benefit to farmers. Although we didn’t know this, artificial selection was discovered by scientists. This is illustrated by the dairy cow. We have been breeding this animal for over ten thousand years. By choosing the cows with the highest milk production, or the largest milk yield, we unconsciously increase their efficiency in making milk. We also alter their biology to produce more meat, and we domesticate them to make sure they are able to tolerate and enjoy human contact. This has many other impacts than just on the dairy cow.
Farmers caught and raised the Auroch, an extinct species for over 400 years. Selective breeding cows was born when farmers began to breed them. It is most likely that the calmest animals can be farmed. They also have more domesticated genes which make it easier to raise them and allow farmers to keep the quieter ones. These genes are only passed on to those who are most suitable for either the environment they were raised in or their intended purpose. This makes farming easier and more efficient. This is not a perfect system. Breeding a cow with a few favorable genes will ensure that they continue to be passed on. Although its phenotype may be favorable, the genes it carries (its geneotype) could be less so. If the positive genotype parent was heterozygous, which means it has a recessive genetic gene that is unfavourable, and the offspring are heterozygous, the chances of the unfavourable recessive recessive genes being expressed in the offspring, is high. This could be a cow with dwarfism or crookedtail syndrome. However, this is a common scenario. To ensure that their offspring have the correct trait, dairy and cattle farmers are able to breed two individuals who possess the same gene. Test crosses are the most common way to identify an animal’s genotype. It involves crossing a single organism that possesses a trait with another. The offspring from this cross can be used to determine if one parent is dominant or non-dominant for the trait you desire. Other methods, such as marker assisted selection (“MAS”), are more recent. They use markers to mark a specific genetic determinant for a trait. This is why MAS is a newer technique in selective breeding. Effectively using the MAS technique involves mapping the gene at the “quantitative-trait locus” or gene in question. This information can be used to aid in marker assisted selection. Linked or very similar genes from the animal’s genome are used to indicate the presence of the desired traits. Crossing over can still occur between these linked or very closely related genes. Therefore, two or more markers are often used to indicate the presence of the desired traits and reduce error in homologous reproduction.
Because we kept the genes that we didn’t need or wanted out of the species, the genetic diversity of the cow has been decreasing since the first domestication. A biological implication is that it may not be possible to breed a gene out due to linked genes. Linked genes refer to genes that are very close to each other on the same genome and have a frequency of less than half recombination. A good example is milk production Citation. Although a farmer might choose a cow with large muscles or a high milk production, there could be side effects such as fertility problems or problems with the immune system. They would all be affected by the same disease if they all died from it.
Cloning is another recent method that allows for the selection or preservation of certain individuals. It’s easy to add additional genes to an individual or species. For example, cows can give their plasma to humans Citation. Transgenesis refers to the process of transferring genes from one animal species into the genomes of another. This can also be done through gene editing or other methods Citation. These cows are being used because they lack blood donors to give plasma to critically wounded patients. Farmers also use their cow’s blood to create extra products or sell them off. This involves replacing the human plasma maker gene with the one in the cow. Scientists remove the ABO gene responsible for plasma generation from the human body, and place it in a cow cell. Next, the cow embryo is electrocuted. This process is very similar to cloning with added gene editing and transgenesis. Depending upon the type and gene of the donor cell (bone-marrow and blood cells), there may not be a 100% success rate. The individual who inherited the genes from their mother or father, and the type of donor cell used, can pass them on to their offspring. That means the 5% success rate is worth it. Because humans are becoming more numerous, we use this technology to save our species.
This could have a biological consequence. It is possible that these gene-edited cows will out-breed normal cows one day. Another reason is that donor cows are only crossed with donor cows. We have been breeding cows for thousands and years to make sure that they are purebred. However, this will reduce the cows’ genetic pool which will in turn make them more susceptible to contracting a single disease. Because not much research has been done on the long-term effects of changing plasma from these cows, it could affect other species such as bacteria or blood sucking parasites, which can impact how other species interact and survive.
It is essential that a species survives long-term. They must have genetic diversity and variation in their gene pool. Without this, they all risk failing to adapt to new conditions or to survive the effects of a pathogen. This is why, despite all the benefits of gene editing and selective breeding cows, the cows may be affected and the entire species could be at risk. The only way to save a species such as the cow that was artificially selected by humans for many thousands of generations is to breed it again. However, transgenesis means that the original animal can continue to exist until the gene-edited one replaces it. Genetic editing can make a species so special that it is impossible to breed with them. This could lead to extinction of something very similar or a shortage or food supply.