We are about to begin one of my absolute favorite curriculum units in the entire world...honestly, it ranks right up there with evolution as some of my favorite stuff to teach in biology. Next week, we begin our study of Mendelian and molecular genetics. And not surprisingly, I've already got fodder for a blog post about it.
Earlier this week, one of your classmates, Angie, sent me a video from youtube about Belgian Blue cattle, otherwise known as "double-muscle" cows. These particular cattle have inherited two mutant copies of the gene (MSTN) which codes for a protein called myostatin. Myostatin's function in vertebrate mammals is well-known--it regulates the growth of skeletal muscle. When MSTN functions correctly, it prevents muscles from growing too large. A mutation of this gene results in muscular hypertrophy, or extreme overgrowth of the muscle. The number of muscles does not actually increase; only their mass increases, resulting in an animal that appears to be Herculean in appearance. A Belgian Blue bull can weigh up to a ton, which is quite a bit larger than your average bull!
Such mutations have been cited in medical literature as having appeared in humans as recently as 2004. A baby boy whose genome contained the defective genes was born in Germany to a mother who was a former professional athlete whose family members had been exceptionally strong. Some scientists have speculated that perhaps the mythological character Hercules may have had this mutation.
Belgian Blues are bred because even though their muscles are large, their meat is tender and lower in fat and cholesterol than traditional cattle breeds' meats tend to be. However, opponents of the practice say that breeding such animals is cruel, and that passing on the mutant gene is unethical.
Breeding of animals and plants because they possess some perceived favorable trait has happened for centuries. It is through this artificial selection of traits that certain genes have been able to persist in the genomes of various species such as cattle, pigs, dogs and plants. It is because of artificial selection that we have corn, broccoli, cabbage and various breeds of dogs, cattle and chickens. Organisms which are bred with this malfunctioning myostatin gene have not only been bred for their lean meat, but also to aid studies of hypertrophic muscle diseases such as muscular dystrophy.
But is it ethical to select for a malfunctioning gene, as in the Belgian Blues? Should malfunctioning genes be selected for? What effect do you think the increase of these genes in the gene pool has on the genome as a whole?
Here's the video, from the National Geographic channel on YouTube. Be warned, there is a graphic depiction of cattle breeding.
Posted by scienceguru on February 21, 2008
Tags artificial selection, better living through biological science, dilemmas dilemmas!, discuss, genetics, what do you think?


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