Ten Facts About the Human Genome

1. Of the 3.2 billion base pairs in the human genome, less than 2% code for proteins. 98% of the genome is not coding for proteins. There are 24000 genes in a human. Rice, for example, has 35000 genes. What is going on? I think I’m more complex than a rice plant.
   
   
2. 99% of the human genome is identical in all people.
   
   
3. The functions of many of the 24000 genes in the human genome are not yet known.
   
   
4. Genome sequencing is getting faster and cheaper. In 2007, the genomes of James Watson and Craig Venter were made public. It took those genomes two months each to get sequenced, with a cost of about 1 million dollars each. The price is going down and down. The objective is to reach the 1000$ genome by the next decade.
   
   
5. Genome sequencing of individuals is useful for: screening for possible diseases, genetic research and origins research.
   
   
6. We have fewer genes than a rice plant. There are three possible explanations for this, but the basic one is that we can do many things with each gene.
   
   
7. Genes are interrupted in their information sequence by non-coding sequences, called introns. Introns are kind of nonsense. Every gene has so many introns that the coding regions can be mixed and matched together. Each human gene gets translated into about 5 proteins.
   
   
8. After a protein is made, it folds into its three-dimensional shape, but other things can happen to it. Sugars can be put on to proteins and change their functions. We can have a set of genes that add sugars to various proteins. These modifications add to the diversity of proteins that can be made.
   
   
9. There is a big chunk of the human genome that makes RNA’s that don’t get out of the nucleus, that don’t end up getting translated into protein. These are very small RNA’s called micro RNA’s (mRNA). They were very recently discovered. In fact, they aren’t even in most textbooks. In the human genome, these small RNA’s may be involved in gene regulation (turning a gene on or off). We’re not quite sure what these mRNA’s are doing, but humans have a lot of them.
   
   
10. Scientists used to say that 98% of the human genome that doesn’t code for protein is junk. It looks like this junk has a valuable function. The junk does have some gems there, the mRNA’s.

The Genome Project History

What is the genome project history? Well, let’s review history. In the closing days of World War II, the United States exploded atomic bombs on the Japanese cities of Hiroshima and Nagasaki. Hundreds of thousands were killed. Many more were exposed to radiation. These survivors, and their descendants, had been intensively studied ever since that time for increases in mutations and their effects on people (especially cancers). By the late 1970’s, methods had been developed to get the sequence of DNA molecules. With this technology, scientists were able to study mutations and genetic diseases in much more detail. In 1984, Nobel laureate Renato Dulbecco made the daring suggestion that we should sequence the entire human genome. If we did that, we could compare the people who were not exposed to radiation to those who were, and we could get a very good handle on genetic damage. It’s not surprising that the first sponsor of what came to be known as the human genome project was the US department of energy, which oversaw the radiation damage project.

The human genome sequence was determined in two ways. There was a huge challenge: chromosomes are extremely long (on the average 100 million base pairs of DNA). Machines could sequence 800 base pairs at a time. So, we cut the 100 million base pairs into 800 bases fragments. How many fragments are those? Well, that’s your assignment. Hint: it’s a lot.

When we determine the sequence of each of those fragments, we just stick them together. Oh, yeah? How are we going to fit them together? How do you know which fragment is which? It’s like taking the Bible, cutting each word and putting them on the floor. How do you line them up?

There were two methods to get some kind of signposts by which we could say “this belongs here”. The methods were called hierarchical sequencing, and shotgun sequencing. Hierarchical sequencing was done by the government sponsored Human Genome Project. This was sponsored by many governments from around the world. Thousands of scientists worked on this effort, and it was led by Francis Collins.

They tried to recognize short sequences of DNA that were at certain landmarks all the way down the chromosome. If that short sequence is on the left end of the chromosome, for example, and then you randomly sequence fragments and you see that short sequence you’ll that belongs on the left end.

It took ten years for scientists to look at all the human chromosomes and get these landmark sequences. Then, they arranged them. It took about 15 years to do this human genome sequencing.

The other way to do it is called shotgun sequencing. Shotgun sequencing was done by private industry, led by Craig Venter. They did the same thing using with landmarks, but they had a computer to find them. This took amazingly sophisticated computer analysis. A whole new field was developed for this shotgun sequencing effort: bioinformatics. This was much more rapid, it took only a year to sequence the human genome.

The complete human genome was finally published in 2003.