![]() ![]() The order of these four base pairs is the genetic code that determines the genotype of an individual. These bases are paired: adenine is paired with thymine, and cytosine is paired with guanine. The handrails are made up of sugar and phosphate molecules, and the steps are composed of four nitrogenous bases: adenine, thymine, cytosine, and guanine. The structure of DNA can be visualized as a spiral staircase. DNA determines the genome, and thus the genetic code, which is a blueprint for development of all body organs and structures. The most common method is some form of crossbreeding.ĭeoxyribonucleic acid ( DNA) is the genetic material that contains the instructions in each cell of organisms. The rate of inbreeding can be reduced, but, if inbreeding depression becomes evident, some method of introducing more diverse genes will be needed. This is not always possible, though, when long-continued selection for the same traits is practiced within a small population, because parents of future generations are the best candidates from the last generation, and some inbreeding tends to accumulate. As a result, producers try to avoid mating related animals. Increased inbreeding is accompanied by reduced fertility, slower growth rates, greater susceptibility to disease, and higher mortality rates. Inbreeding is generally detrimental in domestic animals. These mice are highly inbred so that researchers can obtain the same response with replicated treatments. For example, mice have been bred to be highly sensitive to compounds that might be detrimental or useful to humans. Mild inbreeding has been used in some breeds of dogs and has been extensively used in laboratory mice and rats. Inbreeding is used to concentrate desirable traits. Inbreeding is often described as “narrowing the genetic base” because the mating of related animals results in offspring that have more genes in common. Mating animals that are related causes inbreeding. Because of hybrid vigour, a high proportion of commercial pork and beef come from crossbred animals. In particular, heterosis is thought to be associated with the collective action of many genes having small effects individually but large effects cumulatively. In general, there is more heterosis for traits with low heritability. Such increases generally do not increase in successive generations of crossbred stock, so purebred lines must be retained for crossbreeding and for continual improvement in the parent breeds. This is a common phenomenon in which increased size, growth rate, and fertility are displayed by crossbred offspring, especially when the breeds are more genetically dissimilar. ![]() The other consideration in crossbreeding is heterosis, or hybrid vigour, which is displayed when the offspring performance exceeds the average performance of the parent breeds. Angus produce high-quality beef and Charolais are especially large, so crossbreeding produces an animal with acceptable quality and size. Another example is Angus and Charolais beef cattle. Yorkshires have acceptable rates of gain in muscle mass and produce large litters, and Durocs are very muscular and have other acceptable traits, so these breeds are complementary. An example is the crossbreeding of Yorkshire and Duroc breeds of pigs. Normally, breeds are chosen that have complementary traits that will enhance the offsprings’ economic value. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!Ĭrossbreeding involves the mating of animals from two breeds.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning. ![]()
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