Unlike rice, wheat, and cabbage, which have clear ancestors, there is no wild plant that looks like corn. The earliest records of maize indicate that the plant was developed in southern Mexico 6,, years ago from a grass called teosinte. Scientists believe that early farmers selected only the largest and tastiest kernels of teosinte for planting, rejecting punier kernels.
This process allowed the farmers to develop corn very quickly, as small changes in the plant's genetic makeup had dramatic effects on the grain's taste and size.
Despite their physical dissimilarities, teosinte and corn only differ by about five genes. Today, corn is a staple in diets across the world. Averaged over the years from to , million tons of maize was produced each year around the world, primarily in the United States, China, and Brazil. Without selective breeding, many of the plants and animals on earth today would not exist. However, there are some disadvantages of artificial selection, especially in the case of inbreeding.
Through inbreeding, two closely related organisms reproduce to yield a purebred with desired traits. However, these organisms may also have undesirable traits due to recessive genes found in both parents. Thus, purebred dogs are sometimes born with health defects like hip dysplasia and have shorter life spans than other mixed-breed dogs. Janssens, Luc, et al. Boyko, Adam R. Forest Service. Tigchelaar, Michelle, et al. Farrell, Lindsay L, et al.
Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads. However, in many cases, the most desirable combinations are in heterozygous offspring, meaning the allele for each characteristic will possess one dominant and one recessive gene.
In that case professional breeders have a true breeding cross i. AAbb that provides a gene bank of these qualities that can be crossed with aaBB to reliably produce heterozygous offspring. This process of selecting parents is called artificial selection or selective breeding and has allowed our species to increase the efficiency of the animals and plants we breed, such as increasing milk yield from cows by continuously breeding selected animals with one another to produce a hybrid. However, while it is an advantage to humans to produce these desirable qualities, continuous inbreeding and selection of particular genes runs the risk of losing some of the other genes from the gene pool altogether, which is irreversible.
This is called inbreeding depression, since the overall diversity of the species is reduced. In the long term, it is more advantageous for organisms retain their genetic diversity. Genetic diversity means the gene pool of a species is prepared for a wide range of scenarios such as food shortage or an epidemic of disease. Some genes in some organisms may provide the organism with immunity against various diseases or the ability to go for long periods of time without food.
If continuous inbreeding has occurred in a species, some of these genes may have been phased out due to the breeder wanting other desirable genes to be present in their crop…. Genetic diversity in the long term is reduced, because many organisms end up with similar genomes due to breeding with each other constantly. In normal circumstances, this process would be random and would produce more variable offspring. To ensure the long term welfare of the species they are breeding and their own livelihood, the most important thing for breeders is to keep the gene pool of the breeding stock as diverse as possible while enhancing the traits useful to humans.
With this in mind, humans have gene banks to preserve the genetic information in the case of extinction, and nurture species that are at dangerously low population levels. Ironically, the human interference that has disrupted so many species can now provide a means of placing genes into organisms, therefore preparing them for hypothetical scenarios such as epidemics or climate change.
Genetic engineering would provide the means of allowing organisms to suit their environment without the trial and error over time that comes from natural selection. The next tutorial investigates genetic engineering and the distance it has come.
The first part is identifying the correct ideas that will complete the text. Aberdeen Angus cows have also been bred for their meat. Farmers selectively breed different types of cows with highly desirable characteristics in order to produce the best meat and dairy.
Characteristics can be chosen for usefulness or appearance. Desired characteristics in plants:. Desired characteristics in animals:. The new varieties may be economically important.
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