(REP) Selective Breeding Lesson

Selective Breeding Lesson

What do we mean when say that humans have learned how to manipulate the phenotype of offspring? How are humans able to produce organisms that possess desirable characteristics? What are examples of desirable characteristics? If all modern breeds of dog are descended from the wolf, why do the modern breeds of canines look and act so differently?  

Scientists from the past harnessed the knowledge of genetics, which has resulted in many scientific breakthroughs and uses of this knowledge. Most notably, Gregor Mendel's studies of monohybrid and dihybrid crosses and Charles Darwin's study of evolution and natural selection have meant that humans have learned to actively manipulate the phenotype of offspring by selective breeding in animals and plants.

Breeders of animals and plants in today's world are looking to produce organisms that will possess desirable characteristics, such as high crop yields, resistance to disease, high growth rate, and many other phenotypic characteristics that will benefit the organism and its species in the long term.

Modern farm animals are quite different from those of 200 years ago due to selective breeding. A mutation for short legs arose in a group of sheep from England. Short legs may seem like an undesirable trait for any animal and over time this trait may have disappeared. However, the short legs on the sheep were an advantageous trait for the farmers. They could build lower fences.   The short legs prevented the sheep from jumping over fences and perhaps becoming lost. Farmers would breed short legged sheep until a new breed of short legged sheep was produced. Farmers have also used selective breeding to produce cows that would create large quantities of milk. Selective breeding has also produced chickens that lay larger eggs.  

Sometimes selective breeding can be harmful. Thoroughbreds are horses that have been bred from selected parents to become racehorses. These types of horses even have paper documentation to provide evidence of their genealogy. Thoroughbreds have huge muscles and light bones for strength as well as speed. Selective breeding to produce championship racehorses may have led to Thoroughbreds that are prone to fatal injuries. Inbreeding has led to serious health problems for purebred dogs. Ailments or disorders that are caused by recessive genes are usually masked by the dominant gene. The probability for a gene that causes a disorder to occur is increased when there is no genetic variation. The same genetically similar dogs are mated over and over again. Therefore, the likelihood of a normally rare inherited disorder occurring within purebred dogs is increased. For example, purebred Dalmatians and English Setters can develop an inherited form of hearing loss. Siberian Huskies can inherit a form of cataracts.

 

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