SIMPLIFYING GENETICS

Now that you have decided to look into the field of genetics, I wish you all the brains required to understand it. See, I know it can be hard to learn or understand the so many terminologies and the definitions that surpasses the basic requirements of your interest of research in this field, that's why first I will try to make you feel comfortable as much as possible.

See there are two types of a student in biological science  - one memorizes and the other understands; I want you to understand rather than memorize. I want you to concentrate less on 'Facts' and more on the 'Concepts'. Try to have a conceptual understanding of genetics first before moving forward to memorize the facts. This way, you will surely develop the interest and would not get stressed at all.

For example, I remember when I was pursuing my B. Tech. in Genetic Engineering, one of my professors tried to confuse me by asking "Does the DNA contains the Gene or the Gene contains the DNA?" and I literally got dumbstruck, you know why? Because at that young age I used to memorize the bookish definitions as much as possible without trying to understand what these actually meant. I only knew the definition of 'DNA' as a separate terminology to the terminology of 'Gene'. It was later when I actually understood that 'Gene' is just a coined term for the hereditary information that passes in the process of evolution and 'DNA' or Deoxyribo Nucleic Acid is nothing but the chemical name for it. But yes, if asked we can always say that a gene is a segment of DNA so DNA contains the genes and not the other way around. So basically, DNA is a well observed molecule that contains genes.

Within a biological cell, there is a set of chromosomes made up of chromatin that contains nucleosome beads each made up of 8 histone proteins wrapped up by 147 base pairs (bp) of DNA that contains gene sequences made up of 4 nucleotides A, G, T, C (Adenine, Guanine, Thymine, Cytosine) where A & G are called Purines and T & C are called Pyrimidines - will come later on this....

Thus, this way through this blog, I will try to make you all understand genetics as easily as possible before you start memorizing it to attain those clumsy marks or grades in your class. WISHING YOU ALL THE BEST AND HAVE FUN READING...!!

NOT-SO-FAMOUS CHANNELIZERS IN GENETICS

There have been many scientists who were not accepted by the scientific community in their times even when their theories deduced from their experiments were actually true, take the now-famous Mendel for an example. Similar to Mendel, there were many more scientists who helped channelize "genetics" from the day of its birth up till the "modern genetics" we know today.

Mendel's results implied that some "things" were transmitted from generation to generation. But what was the nature of these things? At about Mendel's death, it was already 15 years left to the completion of 19th century and scientists using ever-improving optics to study the minute architecture of cells coined the term "chromosome" to describe the long stringy bodies in the cell nucleus. But it was not until the early 20th century that Mendel's work and chromosomes came together.

An american medical student, Walter Sutton, realized that chromosomes had a lot in common with Mendel's mysterious factors. Studying Grasshopper chromosomes, Sutton noticed that they double-up almost always - just like mendel's paired factors. Sutton also identified one type of cell in which chromosomes were not paired: the sex cells. Now in his time, DeVries-Correns-Tschermak had already proved Mendel's work to be true and prevalent.; so this was exactly what Mendel had described: his pea plant sperm cells (pollens) also only carried a single copy of each of the factors. Thus, it was interpreted that Mendel's factors, now called genes, must be on the chromosomes.

In Germany, Theodor Boveri independently came to the same conclusions as Sutton, and so the biological revolution began. Their work came to be called the Sutton-Boveri chromosome theory of inheritance. Suddenly genes were real. They were on chromosomes, and you could actually see chromosomes through the microscope.

But not everyone bought the Sutton-Boveri theory, looking down the microscope at those stringy chromosomes, one could not see how they could account for all the changes that occur from one generation to the next. if all the genes were arranged along chromosomes, and all chromosomes were transmitted intact from one generation to the next, then surely many characteristics would be inherited together. But since evidence showed this not to be the case, the chromosomal theory of inheritance seemed insufficient to explain the variation observed in nature. So came by the famous Thomas Morgan, who turned to the fruit fly, Drosophila melanogaster, a little fly that, ever since Morgan, has been so beloved by geneticists.

SO HOW MENDEL GOT ENLIGHTENED?

Mendel realized that there are specific factors - later to be called "genes" - that are passed from parent to offspring. He worked out that these factors come in pairs and that the offspring receives one factor from each parent.

Noticing that peas come in two distinct colors, green and yellow, he deduced that there were two versions of the pea color gene - Y and G - later to be called "alleles". Each parent has a gene that contains a pair of such alleles - in form of either YY (Yellow), YG (Yellow) or GG (Green) - Now how did he say this so confidently? I will tell you why - Mendel crossed a green pea plant with a green pea plant - the result was always a green pea plant (no matter how many generations) but when he crossed a yellow pea plant with a yellow pea plant - the result was a yellow pea plant in the first generation or may be in the second generation too but a green pea plant always use to show up once in a while in the concluding generations. He hypothesized that green version is a recessive version since it needs to be always self fertilized to get a green offspring. Though, it can also get carried away for generations without showing up. Yellow, on the other hand, is the dominant version of a pea plant. It is prevalent, since when he crossed a yellow plant with a green one - the result was either always yellow in the first generation and same in the second generation or sometimes green color used to show up in the first generation itself - in this case - the yellow plant must have been a heterozygous - YG - carrying a green version (G allele) of the color gene.

Thus he concluded that the Green color is the recessive version of pea plant though tends to show up no matter how much you try not to get it; Yellow color on the other hand is dominant version, more prevalent in nature. In order to ease up his mind, he started showing up the heterozygous or homozygous gene pairs as Yy or yy/YY respectively, where 'Y' represents the dominant yellow allele and 'y' represents the recessive gene allele.

Each and every organism which born on the basis of sexual reproduction is either a homozygous or a heterozygous. Albinism is related with the recessive version of the gene that produces skin pigment - melanin. Now just like the Green pea that we prefer to eat, if one prefers an albino to born, both the parents must be an albino but no matter how much we try to avoid, an albino may always show up in one's concluding generations. When a gene is recessive, an individual has to have two copies of it for the corresponding trait to be expressed. Those individuals with a single copy are carriers: they don't themselves exhibit the characteristics, but they can pass the gene on. Therefore, to be albino you have to have two copies of the gene, one from each parent.

Everything was clear, hair color inheritance, eye color, height etc. but the scientific community did not accept it; Apparently, Darwin though living almost in the same era did not got aware of Mendel's work.

Check out the following video for easier understanding of the above concept: -

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.

'TOPSY-TURVY' HISTORY OF THE SCIENTIFIC WORLD

Charles Darwin's theory of evolution, which showed how all of life is interrelated, was a major advance in our understanding of the world in materialistic - physicochemical - terms. The breakthroughs of biologists Theodor Schwann and Louis Pastuer during the second half of the nineteenth century were also an important step forwards. Rotting meat did not spontaneously yield maggots; rather, familiar biological agents and processes were responsible - in this case egg-laying flies. The idea of spontaneous generation was long gone and finally discredited.

However, despite these advances, the theory that the origin and phenomenon of life are dependent on a force or principle distinct from purely chemical or physical forces, a.k.a - vitalism had been lingered on in the earlier centuries. Many biologists, reluctant to accept natural seletion as the sole determinant of the fate of evolutionary lineages had invoke a poorly defined overseeing spiritual force to account for. Physicists, accustomed to dealing with a simple diminished world - a few particles, a few forces - found the messy complexity of biology confusing. Perhaps they had suggested, the processes at the heart of the cell, the ones governing the basics of life, go beyond the familiar laws of physics and chemistry.

This is why the double helix was so important. It brought the enlightenment's revolution of materialistic thinking into the cell. The intellectual journey that had begun in 1500s with Copernicus suggesting the revolution of earth around the sun and not the other way around to Darwin's insistence that humans are merely modified monkeys had finally focused in on the very essence of life. And there was nothing special about it. It was the double helix, the elegant structure. Its message is unimaginative yet a matter-of-fact: LIFE IS SIMPLY A MATTER OF CHEMISTRY.

This emerged a new discipline in science: Molecular Biology, new science whose progress over the last fifty years has been astounding. Not only has it yielded new insights into fundamental biological processes, but it is now having an ever more profound impact on medicine, on agriculture, and on the law. DNA is no longer a matter of interest only to white-coated scientists in an industrial laboratory or some university laboratory; it affects us all.

By the mid-sixties, scientists had worked out the basic mechanics of the cell, and they knew how, via the 'genetic code', the four-letter alphabet of DNA sequence is translated into the twenty-letter alphabet of the proteins - CENTRAL DOGMA - See video below.

The next explosion in the new science's growth came in the 1970s with the introduction of techniques for manipulating DNA and reading its sequence of base pairs. We were no longer condemned to just watch nature affecting us but could actually try to mend with the DNA of living organisms, and we could actually read life's basic script. And now extraordinary new scientific ventures have opened up: scientists would at last treat genetic diseases from cystic fibrosis to cancer; they have also been revolutionizing criminal justice through genetic fingerprinting methods ever since. Scientists are now able to profoundly revise ideas about human origins - about who we are and where we came from - by using DNA based approaches to prehistory. They also have been improving agriculturally important species with an effectiveness we had previously only dreamed of.

"Today, we are learning the language in which God created life. With this profound new knowledge, humankind is on the verge of gaining immense, new power to heal", were the words by U.S. president Bill Clinton in 2000. The genome project was a coming-of-age for molecular biology: it had become big science, with big money and big results. Not only was it an extraordinary technological achievement - the amount of information mined from the human complement of twenty three pairs of chromosomes is staggering - but it was also a landmark in terms of our idea of what is to be human. It is our DNA that distinguishes us from all other species, and that makes us the creative, conscious, dominant, destructive creatures that we are. And here, in its entirety, was that set of DNA - the human instruction book.

However, it is also clear that the science of molecular biology - what DNA can do for us - still has a long way to go. Cancer still has to be cured; effective gene therapies for genetic diseases still have to be developed; genetic engineering still has to realize its phenomenal potential for improving our food. But all these things will come. The future will see many more scientific advances, but increasingly the focus will be on DNA's ever greater impact on the way we live.

WHAT 'WATSON-CRICK' HAD IN MIND AT THAT TIME

In the last century, James D Watson and Francis Crick realized that DNA holds the key to the nature of living things and stores the hereditary information in it, which passes from one generation to the next. It plans this incredibly complex world as it is. Hence they called it the secret of life.

It was already proposed that DNA molecules consist of multiple copies of a single basic unit, the nucleotide, which comes in four forms: adenine (A), thymine (T), guanine (G), and cytosine (C). But its assembly was yet to be unraveled. It was James Watson who in spite of being a younger fellow proposed that (A) can fit neatly with (T), and (G) with (C). He suggested that perhaps the DNA molecule consists of two chains linked together by A-T and G-C pairs.

When Francis Crick heard this from James Watson, he straightaway realized that Watson's pairing idea implied a double helix structure with two molecular chains running in opposite directions. The way they organized the molecule immediately suggested solutions to two of biology's oldest mysteries: how hereditary information is stored,and how it is replicated.

In those days the scientific world was disordered with questions such as: Does life have some magical, mystical essence, or is it, like any chemical reaction carried out in a science class, the product of normal physical and chemical processes? Is there something divine at the heart of a cell that brings it to life? Well! the double helix answered that question with a definitive No.