There is only a 1.6% difference in your DNA and that of a Chimpanzee. Human ethnicities have traditionally been defined by their phenotypes, or physical appearance. Though there are thousands of possible phenotypes for skin color, hair, skeletal structure, and any other physical aspect you can imagine, less than 1% difference exists between all races and ethnicities of mankind. What is it then that cause us to look so different if we all have such similar genes? The answer is found by exploring not the genes themselves, but the expression of those genes.
The phenotype, or the physical appearance, of an individual is a result not only of the genes that the individual possesses. Instead, it is resultant of the genes that the individual expresses. Every individual contains thousands of unexpressed genes. According to a study found in “Nature Genetics”, twenty-five percent of identical genes show different expression levels in Asian and European individuals. Though Asian and European individuals look very different, many of the genes that control their unique hair, facial structure, and many other familiar differentiations are actually created by identical genes, only differing in expression.
Single-nucleotide polymorphisms (SNP’s) located on the regulatory genes are responsible for the majority of gene expression. Think of the SNP as the control panel for a certain gene or set of genes. A single change of one nucleotidea single moleculein the SNP sequence may result in thousands of genes being expressed or not expressed. So changing this one nucleotide may result in a very small change in the overall DNA sequence, but it may result in a much larger change in which genes are expressedsuch as determining if your facial structure if your appearance is Asian or European. Which genes are expressed may also be influenced by gene frequency, dominant and recessive alleles, environmental factors, and a variety of other factors.
A single difference in an SNP may result in drastic differences, and in some cases may result in diseases. Because SNP’s are expressed differently in different ethnicities, this may account for the fact the some ethnicities are more susceptible to genetic disorders such as cystic fibrosis and Tay-Sachs disease. For instance, your chance of being a carrier (someone who has a gene but does not express it) for cystic fibrosis is 1 in 29 if you are of Caucasian descent, while most African Americans only have a 1 in 65 chance or carrying the gene. Asian individuals may have an even more reduced chance of carrying the cystic fibrosis gene, as only 1 in 90 individuals possess the gene [Statistics provided by ACOG Org 2001]. This all links back to the expression of genes.
The study of our genes is a new endeavor for humanity. It was only in 1868 that a young Swiss scientist named Friedrich Miescher isolated a unique compound from the nucleus of living cells. He named the compound nuclein, and it is known today as nucleic-acid. The compound forms the “NA” part of DNA (Deoxyribo-nucleic-acid) and RNA (Ribo-nucleic-acid). It was 1951 before the structure of DNA was uncovered, allowing for the basic understanding of DNA replication to be revealed in 1953.
The Human Genome Project took a total of thirteen years and was completed in 2003. This ambitious project provided identification of 20,000 -25,000 individual human genes, and mapping of over 3 million base pairs. The project also provided insight into function of each gene, and the location of individual genes on the 46 human chromosomes.
Despite our growing knowledge, we still have much to learn about ourselves and our DNA. It is important to understand that our genes contain much more information than is expressed in any one individual. Will it one day be possible to alter the expression of genes in an adult individual? Consider the possibility of altering your eye color on the DNA level, or of curing patients with genetic disorders such as cystic fibrosis. This could one day be possible through control of gene expression.
