The Stubborn Gene

THE BEGINNING OF GENETICS

Genetic diseases has long stalked humanity. The historical chapters of genetic diseases that we are aware of mainly belongs to the royal families that were important to the world in those times. Well, that's just because people use to write about them. But in fact, genetic diseases of various kinds were prevalent before and are now. In reality, genetic diseases aren't the only thing we should be concern of, we have to understand the science of heredity first to monitor the origin and transmission of genetic diseases among generations.

Our ancestors must have wondered about the workings of heredity as soon as evolution endowed them with brains capable of formulating the right kind of question. It was simply understood by many that close relatives tend to be similar, the most productive cows will produce highly productive offspring, and from the seeds of trees with large fruit large-fruited trees will grow. Although apart from enormous benefits and its well use by our ancient farmers it wasn't until in early twentieth century when british biologist William Bateson gave this science of inheritance a name, genetics. Soon, it became an attractive scientific venture but only because of the disputes concerning it in the late nineteenth and early twentieth century.

An understanding of the actual mechanics of genetics proved a tougher nut to crack. Gregor Mendel a. k. a Father of Genetics published his famous paper on the subject in the second half of the nineteenth century but it remained ignored by the scientific community for about forty years. Why did it take so long? After all, heredity is a major aspect of the natural world and more important it is readily and universally observable; a dog owner knows what colored puppies will be produced when a black dog mates with a white or say, brown dog. Even parents subconsciously track the appearance of their own characteristics in their children. One simple reason is that genetic mechanisms turn out to be complicated. Mendel's solution to the problem is not intuitively obvious: children are not, after all, simply a blend of their parents' characteristics. Perhaps most important was the failure by early biologists to distinguish between two fundamentally different processes - Heredity and Development. A fertilized egg may have been contributed equally with its parental characteristics but its development process is a major factor as it requires implementing the genetic information of parents in the offspring or the child. Thus, now scientists have started thinking by taking genetics and developmental biology together.

The Greeks, including the famous Hippocrates, pondered heredity. They devised a theory of "Pangenesis", which claimed that sex involved the transfer of miniaturized body parts: "Hairs, nails, veins, arteries, tendons, bones which were in fact thought to be invisible as their particles are so small. While growing they gradually separate from each other." This was believed till the the end of nineteenth century and in fact the famous Charles Darwin modified the same theory of pangenesis with a new version in which he stated that each organ - eyes, nose, ears, kidneys, bones - contributed circulating "gemmules" that keep on accumulating in the sex organs, and were ultimately exchanged in the course of sexual reproduction. Because he believed that these gemmules were produced throughout an organism's lifetime, he also believed that any change that occurred in the individual after birth, like the stretch of giraffe's neck imparted by craning for the highest branch of leaves, could be passed on to the next generation. So he, in one aspect, believed the famous Lamarck's theory of inheritance of acquired characteristics with giraffe as an example but he still emphasized more on the natural selection as the reason behind inheritance and not the organism's will. It is a bit suspicious but it is said that Mendel's work although done in the same time never came in view of the famous Darwin.

By the early nineteenth century, better microscopes defeated the theory of preformationism (presence of a tiny homunculus in sperm which enters the egg and grows in size) and the Darwin's theory of pangenesis. And eventually both the theories laid to rest by August Weismann, who argued that the inheritance depended on the continuity of germplasm between generations and thus changes to the body over an individual's lifetime could not be transmitted to subsequent generations. His simple experiment involved cutting the tails off several generations of mice. If Darwin's theory or Lamarck's theory is to be believed then new offsprings in mice generations should have small or no tail at all.

Gregor Mendel was the one who got it right. Unlike the other biologists of that time, he approached the problem quantitatively. Rather than simply noting that crossbreeding of red and white flowers resulted in some red and some white offspring, Mendel actually counted them, realizing that the ratios of red to white progeny might be significant - as indeed they are. But since Mendel wasn't able to replicate his results with a different plant, his work was never appreciated by the scientific community of that time, it was in the 1900s when rediscovery of Mendel's work took place by three different botanists independently: DeVries, Correns, and Tschermak. They helped expand awareness of the Mendelian Laws of Inheritance in the scientific world.