Researchers can use DNA sequencing to search for genetic variations and/or mutations that may play a role in the development or progression of a disease.

The disease-causing change may be as small as the substitution, deletion, or addition of a single base pair or as large as a deletion of thousands of bases. The speed of sequencing is increasing and the cost continues to decrease. This will lead to a greater ability to use this technique.

What We've Learned So Far

One of the greatest impacts of having sequenced the human genome may well be in enabling an entirely new approach to biological research. In the past, researchers studied one or a few genes at a time.

With whole-genome sequences and new high-throughput technologies, they can approach questions systematically and on a grand scale. They can study all the genes in a genome, for example, or all the transcripts in a particular tissue or organ or tumor, or how tens of thousands of genes and proteins work together in interconnected networks to orchestrate the chemistry of life.

What Does the Human Genome Sequence Tell Us?

By the Numbers

		The human genome contains 3,164.7 million chemical nucleotide bases (A, C, T, and G). The average gene consists of 3,000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases. The total number of genes is estimated at ~21,000 - 25,000. Almost all (99.9%) nucleotide bases are exactly the same in all people. The functions are unknown for over 50% of discovered genes.
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The Bottom Line

During the past 50 million years, a dramatic decrease seems to have occurred in the rate of accumulation of repeats in the human genome.

Repetitive sequences are thought to have no direct functions, but they shed light on chromosome structure and dynamics. Over time, these repeats reshape the genome by rearranging it, creating entirely new genes, and modifying and reshuffling existing genes.

		Less than 2% of the genome codes for proteins. Repeated sequences that do not code for proteins ("junk DNA") make up at least 50% of the human genome. Other areas are still being studied to determine their role.
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Variations and Mutations

The information on genomic mutation and variation promises to revolutionize the processes of finding correlations for disease-associated gene sequences.

Scientists have identified about 1.4 million locations where single-nucleotide polymorphism (SNPs) mutations occur in humans.

		The ratio of germline (sperm or egg cell) mutations is 2:1 in males vs. females. Researchers point to several reasons for the higher mutation rate in the male germline, including the greater number of cell divisions required for sperm formation than for eggs. This may account for why men have a greater likelihood of getting cancer. This image courtesy of Genome Management Information System, Oak Ridge National Laboratory