Eurie Hong, Ph.D.
Head Curator
Saccharomyces Genome Database

Abishai, OR, US

By what percentage do the DNA sequences of two humans differ? What are the mean and standard deviation of the distribution of pairwise DNA-sequence differences between two random human beings?

Eurie Hong
Head Curator,
Saccharomyces Genome Database,
former HHMI predoctoral fellow
In general, the DNA sequences from the genomes of two random human beings will be >99% similar. The differences between two individuals can be measured by the following types of variations:

1. Changes in a single base pair, also known as single-nucleotide polymorphisms (SNPs). On average, there is a SNP every 1 in 100-300 base pairs.

2. Small insertions or deletions.

3. Copy number variations, which are differences in how many copies of a gene individuals carry.

The number of fully sequenced genomes from individuals is limited, so it is difficult to assess an "average" variation. More information about the extent of variation among individuals will be known as more individuals are sequenced.

Several major public and private efforts are under way to sequence full genomes of individuals and identify biologically significant SNPs. Here are some useful and interesting links about projects measuring variation:

HapMap Project: http://www.genome.gov/10001688

Copy Number Variation Project: http://www.sanger.ac.uk/humgen/cnv/

1000 Genomes Project: http://www.1000genomes.org/page.php

More information about SNPs:

http://www.ornl.gov/sci/techresources/Human_Genome/faq/snps.shtml

02/25/10 17:39