Similar anomalies are rare because new case has received a separate scientific articles in the Journal of Fish Biology. Researchers from Michigan State University, explains that scientists are much more likely come across two-headed lizards and snakes, but it may not reflect the true picture.
"These animals, — says Michael Wagner, an assistant professor and one of the authors of the opening — often bred in captivity, so the appearance of anomalies easier to detect."
Sharks, unlike snakes and lizards, very rare breed in the eyes of man, and two-headed birds usually live very long, and do not grow to adulthood.
The described specimen was removed by one of the fishermen catch a female bull shark and penetrated her womb. These large fish are viviparous, they appear at times to 13 fry and fish length at birth is about 60 cm (adult — 3.5 meters). Two-headed specimen was delivered to researchers and those do not even dare to open a unique discovery: in order to keep her safe and sound, biologists have used magnetic resonance imaging.
CT scan showed the presence of two different hearts, stomachs, and naturally all of the above. But the tail of the individual (or individuals?) Was a common — a detailed study of these rare specimens may help to understand the general laws of development of embryos and shed light not only on the abnormal, but also quite normal physiological processes. The study genetics of fruit flies with extra legs instead of eyes at one time possible to discover the genes responsible for the definition of the axis of the embryo as a "head-to-tail" as well as more subtle divisions — Hox genes are responsible, for example, for the development of the fingers on the limbs.
Ecology nothing to do with
Separately, Wagner warns that should not be linked to the discovery of environmental pollution. Yes, the fish caught in the Gulf of Mexico, where previously there was an oil spill. But "after" does not mean "due" — as has been said, many animals regularly produces such two-headed calves and under the most favorable conditions. Moreover, even a man about a third of all fertilized eggs do not even leave the womb of its embedding in the wall — and the reason are including developmental abnormalities, in all animals, including you and me, is integrated natural defense mechanism of the development of critical errors.
Incidentally, congenital anomalies
like a two-headed or irregularly shaped limbs — not necessarily mutation. Furthermore, mutation are not identical hereditary disorders, so in the text above you will not see any proposal about the "shark caught by scientists of the mutant." Let's start with the mutation as the most popular concepts.
Who are the mutants? We are with you.
Mutations are changes in DNA that is not so rare as commonly thought — any of their newborn child has about fifty of 3.5 billion base pairs, and most mutations are harmless and does not manifest itself. Even some of the harmful or lethal, but some, on the contrary, benefit. Or, what happens too often, it may be useful in certain circumstances. The people of Africa, for example, is often found a gene that increases the resistance to malaria — but it increases the risk of sickle-cell anemia.
Each gene exists in several forms (alleles are said to genetics) and often can not tell which one is "better." The risk of malaria, or the risk of anemia — which is worse? High probability of melanoma or a deficiency of vitamin D? Now some bad genes, causing, for example, susceptibility to Alzheimer's disease, could save a thousand years ago from a long-forgotten disease, and natural selection acting on the people of South Africa, hardly imagined their resettlement in cloudy northern countries.
Where are the ugliness?
Two-headed fish could occur without any genetic anomalies — just at the right time embryo cells divided once again, or not moved to the right place. Such failures are rare, but not impossible, their likelihood increases when exposed to certain chemicals — a notorious example is talidomidovaya disaster. It is important to understand that such violations can not be inherited!
Inheritance without mutations
Relatively recently shared genetics and hereditary genetic diseases. All of our cells exactly the same set of genes, but in a particular tissue, they include only those genes that are necessary for a specific task — the cells of the heart does not need enzymes of the liver cells or the more hard shell osteocytes, bone cells. Each gene can be turned on or off by the reversible (in contrast to mutations!) Chemical moditsikatsii restructuring of chromosomal DNA or proteins.
These "switches" are inherited and proved that in some cases such an inheritance increases the risk of certain diseases. Maternal smoking during pregnancy may increase the risk of asthma is not only the child, but also grandchildren — at least, demonstrated a similar effect in rats.