Example of selective breeding. The Aberdeen Angus bull is bred for beef. The Friesian cow is a dairy breed. The traditional Highland cow. Selective breeding takes place over many generations. As a result, many dog breeds have vastly different appearances. Think of the Chihuahua and the Dalmatian — they're both dogs, but they share few physical attributes. This degree of difference in a single species is a unique phenomenon in the animal world.
Selective breeding has also been practiced in agriculture for thousands of years. Almost every fruit and vegetable eaten today is a product of artificial selection. Cabbage, broccoli, cauliflower, Brussels sprouts, and kale are all vegetables derived from the same plant, Brassica oleracea , also known as wild cabbage.
By isolating wild cabbage plants with specific characteristics, farmers were able to create a variety of vegetables from a single source, each with different flavors and textures. Broccoli, for example, was developed from wild cabbage plants that had enlarged flower development while kale was derived from Brassica oleracea with larger leaves. Corn, or maize, is an unusual product of selective breeding. 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. For example, chicken breeding companies have used an X-ray unit called a lixiscope to identify subclinical leg bone abnormalities in meat chicken breeding stock, allowing them to actively select against its presence in breeding stock, thereby improving overall leg health in meat chicken breeds — funnily enough, the lixiscope was in fact developed by NASA scientists!
Meat chicken breeding companies have also used a technique called pulse oximetry to measure the oxygen saturation levels in the blood of chickens, an important indicator of susceptibility to several metabolic diseases, in order to develop breeds which have stronger cardio-vascular and respiratory systems. But will the Australian chicken industry ever use breeds of chicken derived from GM technologies? The focus of meat chicken breeding programs has itself evolved quite dramatically over the years.
In the s, the goal of selective breeding in meat chickens was basically all about increased growth rate and increased meat production i. These days, the approach is much more balanced, with health and welfare very important breeding targets. This is illustrated in the figure below, which I have extracted from the ACMF website and which compares the breeding goals of a major meat chicken breeding company with its goals in This shows that the focus has changed from growth and yield to a broad spectrum of outcomes, with a clear emphasis on improving animal welfare, reproduction and fitness outcomes.
Consumers have benefitted from the improvements in productivity that have resulted from the gains made through selective breeding, particularly in terms of lower prices for chicken meat, greater availability of chicken meat, and more consistent quality. Previous Next. In an earlier blog, I described how modern meat chickens have been selectively bred to grow well and put on a lot of muscle meat , in the context of explaining that these characteristics have been achieved without the use of hormones hormones not having ever been fed or in any way administered to meat chickens in Australia for over 50 years — see: Chookchat — the hormone myth In another blog, I explained how different selective breeding paths had led to separate chicken breeds for commercial meat chickens and egg laying chickens which not only perform very differently one grows to a large body size and carries lots of meat; the other produces lots of eggs , but which also look quite different too.
Selective breeding — why? What controls whether we inherit a specific trait? Some traits are controlled by many different genes, and we might not inherit them all. So, how can understanding DNA be useful in agriculture?
Modern genetic techniques allow farmers to identify the specific gene or genes that controls a desirable trait. Using these techniques, breeders can quickly identify which organisms have desirable genetics without having to wait for them to reach adulthood and display specific traits. This is particularly useful for traits that are difficult to measure, such as disease resistance, or those that are largely controlled by the environment.
It also means that multiple genes can be identified at the same time. This makes it easier to select for traits controlled by several different genes, or to select organisms with a combination of different traits. However, even with these molecular tools, selective breeding can only get us so far. In most cases, a trait can only be bred into a population if it already exists within a species.
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