Genetic markers are segments of DNA that can be used to trace patterns of inheritance. Genetic markers may or may not have any genetic function. In higher organisms, well over 90 percent of the DNA conveys no genetic information. Noncoding DNA, while not useful as a source of genetic information in cells, can be used by scientists to trace genetic ancestry.

Chromosomal DNA is reshuffled each generation, as meiosis separates pairs of chromosomes, and fertilization brings them back together in new combinations--one chromosome from the mother, and one from the father, in each pair. Chromosomal DNA, therefore, is inherited by complex routes through both the mother and the father. However, DNA within mitochondria is inherited only from the mother, and DNA of the Y chromosome in humans is inherited only from the father.

Agriculture entered Europe from the Middle East about 7,500 years ago. Historians have debated whether this occurred because of a progressive invasion of Europe by farmers from the Middle East, or because agricultural techniques diffused from one population to another from the Middle East. Analysis of genetic markers from skeletons of the earliest farmers showed little similarity of their mitochondrial DNA with that of modern Europeans. Modern European males have Y chromosome markers that resemble those now common in the Middle East. These facts suggest that immigrant Middle Eastern males mated with resident females in Europe about 7,500 years ago, bringing agriculture with them.

Three famous examples of the use of DNA markers are the identification of the remains of the last czar of Russia, Aaron's Y chromosome, and Thomas Jefferson's descendants. . .

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