Given all the variety that exists among human beings, it often comes as a surprise to learn that all people share over 99% of their genes.
The variations, both visible and otherwise, are the result of differences in the remaining 0.
1% of genes.
To get an idea of how this is possible, keep in mind that humans have a 95% to 98% similarity to chimpanzees, depending on the method used.
Most genes are used to create things like red blood cells, nerves, bones, and other basic components found in all animals and are, therefore, going to be the same between species.
Still, the handful of unique genes have a powerful impact on how individuals turn out.
Basic Structure Before looking at individual differences, it helps to get an idea of how genes are structured within human cells.
Physically speaking, genes are contained in a molecule called deoxyribonucleic acid or DNA.
This molecule consists of only four active chemicals, adenine, guanine, cytosine, and thymine which are arranged in pairs.
However, DNA possesses just 3 billion of these paired molecules called base pairs which are strung together in a particular order.
These strands are twisted into a double helix to form the familial DNA molecule.
That double helix is then rolled and balled up into a chromosome.
Variable-length sections of these DNA strands constitute genes.
The genes are determined by whether a particular segment is involved in one or more protein-producing functions.
Since identifying which segments might be involved in this or that operation is an on-going area of research, the current figure of 24,000 human genes is still an estimate.
The Power of Genes The accepted number of genes that vary between individual humans is 0.
1%.
Some studies using different methods indicate it might be as high as 0.
4%, though.
This percentage translates into roughly 3 million base pairs.
Interestingly, only about 1% of these base pairs actually constitute genes that perform work.
The remaining 99% is considered junk DNA.
This junk DNA is still heritable and is used to determine one's ancestry.
As might be expected, trying to analyze 3 billion base pairs would be a very daunting task.
Instead, biologists may focus on particular regions of the chromosomes called short tandem repeats (STR's) or microsatellites.
These regions are made up of several base pairs that repeat up to 100 times and possess a high level of variety.
Microsatellites are used primarily to match DNA samples to individuals.
Just Like Dad While microsatellites are useful for identifying individuals, they're not as good for tracing ancestry.
The problem is that with each generation, microsatellites from both parents mix together and create new, distinct ones in the offspring.
STR's on the other hand are passed down unchanged unless there was an error or mutation in the replication, which is very rare.
One of the chromosome pairs doesn't follow this typical pattern, though.
The X-Y chromosome pair undergoes little alteration because the Y chromosome inherited from the male line is very different from the female X chromosome.
Examining microsatellite markers on the Y chromosome show a male individual's paternal lineage.
In the case of females, a separate unit of DNA called mitochondrial DNA is used to establish maternal ancestry.