Human Genome

Human Genome

On Monday 26 June 2000, after more than a decade of effort, a working draft of the human genome was presented to the humanity. This day would be remembered as the day when humankind learned about the set of genetic instructions which governs the assembly and fuction of human beings.

The scale of this triumph of biological science is awesome.

  • The 24 different human chromosomes may be too small for the eye to see, but each set contains 3.1 billion base pairs: a code written in 3.1 billion “letters”. This amount of data is equivalent to the contents of 200 telephone directories, each 500 pages long. It has been estimated that it would take over nine years to read aloud this data.
  • If all the DNA in the human body were put end to end, it would reach to the sun and back more than 600 times.
  • There are 20 different building blocks (amino acids ) used in an array of combinations to produce proteins as different as keratin in the hair and haemoglobin in the blood.
  • The vast majority of the DNA (97 % ) in human genome has no known function.
  • Between humans the DNA differs by only 0.2 %.
  • Human DNA is 98 % identical to chimpanzee.
  • Scientists estimate that there are 300,000 spots in the human genetic code where individual differences can exist.

Reading Human genome code took the combined efforts of thousands of researchers, and countless hours of work by hundreds of state-of-the-art robotic sequencing machines humming quietly around the clock in pristine laboratories. Each machine prepares DNA samples, runs them through electrophoresis gels, and reads off the results into a database, only requiring the help of a human once every 24 hours.

The public Human Genome Project took blood and sperm samples from a dozen anonymous donors and combined them. The project’s commercial rival, Celera Genomics, put an ad in The Washington Post, selected 30 men and women from a variety of ethnic backgrounds and used six of them.

Estimated number of genes:
Humans & mice – 60,000 to 100,000
Roundworm – 19,000
Yeast – 6,000

October 16, 2002
Researchers have come up with some new findings. That the genome has revealed  that the human chromosome carries only about 30,000 genes, twice the number of a fruit fly, 10,000 more than a roundworm, and only a few hundred more than a mouse. Originally scientists expected as many as 140,000, which means the question of how genes actually work is now an even bigger mystery. The genome also reveals that many human genes originate from microbes. This raises questions about human evolution.

In future:

  • Doctors may treat you for conditions such as cancer and heart disease even before they appear. There may be fundamental shift towards preventive medicine.
  • A routine check-up in future will perhaps involve giving a sample of blood from which your DNA will be extracted and screened to determine your risk of developing various diseases.
  • We already know the genes that cause many rare, single-gene disorders, but in future you could be screened for common diseases that appear in adulthood, such as type II diabetes, heart disease and cancer, and perhaps even complex mental disorders such as schizophrenia and depression. Because these diseases have many contributory factors, both genetic and environmental, the test results will give a percentage risk rather than a definite yes or no.
  • Doctors may also use gene screening to discover which drugs best suit you. Our genes determine whether different drugs will work well or cause side effects. For example, Alzheimer’s patients with a gene variant called ApoE 4 are much less likely to benefit from a drug called tacrine than other patients.
  • The insurance agencies making use of genetic information is a possibility.
A single gene may play a role in the development of cancer and a number of age-related diseases, including arthritis, hardening of the arteries and Alzheimer’s disease, according to new study findings.
Gene Therapy
Genetic disorders
Genome Sequencing helps diagnosing rare disorder