Tag Archives: Genetics

Editing Genes Using Molecular Scissors

Friends,

In the last few years a revolutionary new technique has been developed to edit genes. In this VERITAS I will describe the technique and how it has the potential to completely transform the way we fight diseases and how it may help us come up with new disease resistant varieties of plants and animals.

Continue reading Editing Genes Using Molecular Scissors

Epigenetics and the Resurgence of Lamarckism

 

              We have all learnt the basics of genetics and Darwin’s theory of evolution in our schools. We learnt that evolution is a slow process and changes to a species in response to changing environmental conditions takes place over many generations( 100s possibly). We also learnt that sometimes there are random genetic mutations in our DNA- these are very small in number( less than 0.001% of our genes). Over many generations some individuals carrying these mutations becomes more suited for survival in the environment. That set of individuals survives and the others perish or their numbers decreases and slowly over many many generations the species evolves.

 

                Today I will tell you about a remarkable new subject which changes all this. The interesting thing is that this new and amazing subject revives a very old theory of evolution.

 

                In 1809 the French biologist Jean-Baptiste Lamarck proposed that an organism can acquire new characteristics during its life and these can be passed on its offspring. He proposed that if an organism uses a part more, that part grows in size or becomes strong and the increased size/strength can be passed on to its offspring. Similarly if an organism does not use a part, that part becomes smaller or weaker and that characteristic is passed on to its offspring. In the offspring also that particular part will be smaller or weaker. Lamarck used his theory to explain the long necks of giraffes.

 

                Note that Lamarck proposed this theory much before Darwin’s theory of natural selection which was published in 1859. Darwin’s theory was completely different from Lamarck’s theory. Darwin’s theory tells us that if an individual adapts to his environment that adaptation is not carried forward to the subsequent generation. Later Mendel’s experiments gave the mechanism behind Darwin’s theory and that resulted in the modern theory of evolution and genetics. So according to this theory if an individual uses a part of his body more, that part may become stronger during the life of the individual but that strength is not carried forward to the subsequent generation. The subsequent generation just gets the father and mother’s genes without the information as to how their lives was lived. No information as to how the individual adapted to its environment is carried forward. Lamarck’s theory was nearly forgotten and Darwin-Mendel’s theories became modern genetics.

 

                Scientists even gave this principle a name: Weismann barrier. So the Weismann barrier refers to the principle that information flows from the genes to the rest of the body and never is reverse. To be more precise, information only flows from germline cells(genes) to the somatic cells(other cells). So modern generics believe that the Weismann barrier cannot be penetrated. So what we experience using our sensory organs cannot affect the genes because it cannot penetrate the imaginary Weismann barrier.

 

                In the last few years scientists have analyzed new data which could not be explained by modern genetics. A group of scientists studied the population of a region in northern Sweden over several generations. This region had many years of famine in the 19th century. And there were several years of abundant harvest and food. The scientists studied life expectancy of many generations and tried to associate it with the famine and food abundant years. They found that the children of people who had gone through even one year of famine had a different life expectancy from children of people who had never seen a famine. Children of people who enjoyed over abundant food lived less longer than children of people who had seen famines. So the adaptation to food scarcity had carried on to future generations! The amazing thing is that even if a person had seen a famine year in his childhood, his child will have an increased lifespan. The complete data is too large to write here but the important point is that what we experience in our lives does get carried over to our children.

 

                Where is this information carried? In our genes? NO! Our genes remain the same whether we smoke or not. Our genes do not change depending on whether we do intellectual work or not. Our genes do not change if we starve. This information is carried in how the genes express themselves. So the same genes may express themselves differently in different people. Thus this subject is named epigenetics- beyond genetics.

 

                Over time evidence for more epigenetic factors were found. One experiment showed that if an individual smoked his children are more prone to obesity and shorter life spans. We are not talking about a mother smoking during pregnancy. We are talking about smoking much earlier in life. And this happens even if the father smoked much earlier in life- even before adolescence-even before the first sperm cells were formed. So the observation was that smoking causes a change in the gene expression though it does not change the genetic makeup of the individual. And this gene expression can be carried on to future generations.  How many generations? Not forever like the genes. But it can be carried over up to 15 generations.

 

                How does this work. One of the most common mechanisms is DNA methylation. When a methyl group attaches itself to a gene, it can change the gene expression. It can make it “louder” or even “silent”. The gene may be the same but what you do in your life may change how it is expressed. And this expression is carried forward. Another Epigenetic technique is known as genomic/genetic imprinting. We have already read about it in an earlier VERITAS when we found out why Ligers are much larger than Lions and Tigers while Tiglions are much smaller than both. ( See VERITAS: Liger, Tiglon and Genomic Imprinting Jan 14, 2010. Available at http://unvarnished-veritas.posterous.com/liger-tiglon-and-genomic-imprinting)

 

                Epigenetics is a very exciting new area of research. It gives us a good news and a bad news. First the bad news. Don’t just blame it on the genes. We are passing on not just the genes but also how they will be expressed to our children. We may not have control over the genes but we do have some control over the epigenetic factors. Now the good news: These new discoveries are opening up new areas of research- How can we make drugs that turn down the expression of certain harmful genes. Maybe epigenetics will bring us the next generation of cancer or Alzheimer drugs.

 

                So it turns out that though Darwin was not wrong but Lamarck was also right. Darwin was telling us about how genetic evolution takes place. And Lamarck was telling us how our lifestyles change the epigenetic factors and that they can be inherited.

 

                It is such a beautiful and interesting world out there. The only tragedy- life is short!

 

 

Regards

Kanwar

 

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Go wondrous creature, mount where science guides

go measure earth, weigh air, state the tides,

instruct the planets in what orbs to run

correct old time, regulate the sun

======================================================================

Liger, Tiglon and Genomic Imprinting

Friends,

 

            A few days back I read about two very interesting animals- the liger and the tiglon. In this VERITAS I will tell you about these animals and also about a very interesting fact of genetics that makes these animals so different from each other.

            A liger is the offspring of a male lion and a female tiger. So it is a hybrid of a male lion and a female tiger. They are much larger than both lions and tigers. Ligers are the largest cats in the world! It takes the best characteristics from both parents. It is very sociable like lions and like tigers, it loves swimming. Of course, lions and tigers would never mate in the wild. So a liger are typically born of captive lions and tigers.

            A Tiglon is the offspring of a male tiger and a female lion. It is much smaller than both the lion and the tiger.

            Let’s compare the sizes of these animals: a lion is about 8 feet in length and weighs about 250 kg. A Tiger is about 10 feet in length and weighs about 300 kgs. A Liger is about 12 feet in length and can weight upto 500 kg. So a Liger is about twice the size of a Tiger or a Lion! A Tiglon is about half the size of a Tiger and weighs about 160 Kgs.

 

            That brings us to the most interesting question: when both are offspring of a tiger and a lion then what causes Ligers to be huge and Tiglons to be so small in comparison? The answer is amazingly interesting and due to a very interesting generic phenomena called genomic imprinting.

 

We inherit two copies of every gene: one from our mother and the other from our father. Usually both genes are active. It is true that the characteristics produced by these genes may show a particular domination but that is because the effect of one gene overrides the effect of the other. Both genes are active. But in a very small number of genes, one copy is turned off depending on whether it came from the mother or the father. So the fact that the copy came from the mother or father is “imprinted” on these genes and that turns it off or on. So for most genes, there is no information regarding which parent it came from. But some genes behave differently depending on whether they came from the mother or father. These genes have their “source” imprinted on them and that makes them turn off or turn on. In the human genome there are about 23000 genes out of which only 80 are imprinted.

 

Now, lets look at how Lions live. They live in prides. There are several male and female lions in a pride. Now, each male lion wants his offspring to be the biggest and most powerful. Only then would his future survival in the pride or group be assured. So an imprinted gene from the male lion promotes growth- an extraordinary growth. But the lioness’ concern is different- she will give birth to several cubs at once and does not want any one of them to grow at the others’ expense. Also a larger cub would mean danger for her also. So there is an imprinted gene from the lioness that curbs too much growth. When a lion and lioness mate and produce an offspring, the growth enhancing gene of the male lion is countered by the growth diminishing gene from the lioness to produce “normal” sized cubs.

 

Lets now look at how Tigers live. They are solitary creatures. Since they do not live in prides so male tigers do not have the “super-growth” imprinted gene. There is no question of competition within the group. And since male tigers do not have the “super-growth” imprinted gene so the tigress does not need the growth diminishing imprinted gene.

When a male lion mates with a tigress, he gives the “super-growth” imprinted gene. But the tigress has nothing to counter it. So we get a liger- a huge creature that the tigress finds it difficult to deliver naturally. Frequently a c-section is required to deliver this giant which becomes much bigger than a lion or a tiger.

 

When a male tiger mates with a female lion, he does not have a “super-growth” gene but the lioness has a growth diminishing gene which diminishes the growth of the offspring unchecked producing the much smaller tiglon.

When I first read the reason, I was delighted and amazed at the same time. It was 2 AM in the morning and I could not control my excitement at such an interesting fact! Knowledge is a great source of joy. In fact, the greatest source of joy!

 

Curioser and Curioser,

Kanwar

 

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Go, wondrous creature! mount where Science guides:

Go, measure earth, weigh air, and state the tides:

Instruct the planets in what orbs to run,

Correct old time and regulate the Sun;

 

=================================================================

 

 

Human Genome Project

Before I start today’s VERITAS I am reminded of a few lines by Goethe which run opposite to the subject of today’s VERITAS :

 

      He who would study organic existence

      first drives out the soul with rigid persistence

      Then the parts in his hands he may hold and class

      but the spiritual link is lost . Alas !!

                              Goethe ( Faust )

 

                  The Human Genome Project

                  =========================

 

Each of our cells contain 23 pairs of chromosomes . One set that we got

from Dad and another we got from Mom . Each of these chromosomes contain

genes . These genes control the way we look , behave etc . These genes

are a sequence of chemical building blocks represented by letters :

A( adenine ) , T(thymine ) , G(guanine) , C(cytocine ) . So you get a pair

of genes of each characteristic ( one from Mom and another from Dad ) and

one of them dominates and decides the way we are .

 

 

In 1990 a project was started to study each of the chromosomes and find

how many genes each contains and where they are on the chromosomes and

what their functions are . This is called The Human Genome Project .

The task was huge . There are approximately 10,000 human genes and

each has a long chemical structure . The project should be finished in 2003.

If the entire DNA sequence of an individual is written is a book it

would have 200 books of 1000 pages each . It is that big .

 

 

At the end of all this we would know what diseases are caused by what

gene . What each gene is responsible for and how we can treat ourselves

genetically . But most importantly we will be able to understand ourselves

from a basic chemical level .

 

 

How far has the project progressed ? The 5th , 16th , 19th , 21 st and the

22 nd chrosomes have been completely mapped( studied ) . The rest of

the chrosomes are beiong studied parallely at different labs in the world .

 

 

      The first chromosome to be completely studied was the 22nd . THis

was because of its small size . It reveled 545 genes and 134 pseudogenes

( these are genes that once functioned but no longer do ) .

 

      One very important development occurred when the 21st chrosome

was decoded . It contains 225 genes . Mutations in 14 known genes of

this chromosome cause diseases like Alzeimer’s syndrome , epilepsy .

And this may be a boon to control these diseases before they occur

in individuals ( right at the embroyonic stage ) . Mutation is some kinda

garbar in sequence of a gene . Another disease we may control by the

map of the 21st chrosome is Down’s syndrome which is responsible for

mental retardation in one out of every 700 kids .

 

      The Human Genome project is funded by Department of energy US

and has scientists all over the world working on it . IT also maintains

a very inteseting website : http://www.ornl.gov/hgmis . You can even see

some chrosomes and see the sequences . Amust see !