Understanding Genetic Genealogy

The Seven Daughters of Eve by Bryan Sykes

Oct 21, 2008 Sara E. Lewis

Sykes says his book is about "the history of the world as revealed by genetics." He tells his research story in a easy way that serves to demystify his conclusions.

The Seven Daughters of Eve is a must read for anyone considering analysis of DNA to supplement genealogical research. Sykes conversational tone and breezy writing style demystifies the science. Almost without knowing it, the reader will gain vocabulary and knowledge that makes his or her personal adventure in genetic genealogy much easier to understand and appreciate.

From Genetic Disease to Genetic Dating

As a professor of genetics at the Institute of Molecular Medicine in Oxford, Sykes studied brittle bone disease. Researchers had found it was caused by changes in the genetic code for collagen, the protein that reinforces bones. If something is wrong with collagen, bones break.

Through his work he met professionals who were carbon-dating bones for archaeological work. To get more information from the bones, they extracted and amplified DNA from the mitochondria of cells and studied the sequence of amino acids that made up the proteins. The successful recovery of DNA from the ancient bones sparked his future work.

DNA Codes Life

Children look like their parents and this is due to information carried by genes, pieces of genetic coding inherited equally from both parents. Gregor Medel laid the foundation for genetics with his experimental breeding of peas. Although it was known by the mid-19th century that chromosomes were the messengers of heredity, it wouldn’t be until 1952 that scientists solved the molecular structure of deoxyribonucleic acid or DNA.

DNA is made up of four components known as nucleotide bases. The four arrange themselves in many ways to create pure and simple information. It instructs other processes. “The cellular middle managers, which receive the instructions and do the work are, it turns out, the proteins,” says Sykes. “They might look sophisticated, and they are; but they operate under strict directions from the boardroom, the DNA itself.” Proteins are made up of sub-units called amino acids, whose precise order dictates their function.

Blood Transfusions Figure in Development of DNA Understanding

The first blood transfusions were recorded in Italy in 1628, but many people died due to severe reactions, so they were banned. Differences in blood types were soon discovered and it was noted that the differences were causing the problem. The nature of the reaction was first discovered in 1875. After the First World War, blood group data was compiled from transfusion centers. After the Second World War, researchers began to unravel the complicated genetics of blood types. They began to understand the process of gene mixing.

Differences in DNA Noted

A 1987 paper discussed how the author had used mitochondrial DNA to show how human populations have evolved. If two people have a very similar mitochondrial DNA, then they are more closely related. They have a common ancestor who lived more recently in the past. People with very different mitochondrial DNA share a more remote common ancestor. Both males and females have mitochondria in all cells, but only women pass theirs on to offspring because only women produce eggs. Fathers pass on nuclear DNA.

Differences in DNA

At conception, DNA from the parents is recombined and copied. In the process changes may occur as simple mistakes in copying. Researchers discovered a region of mitochondrial DNA that has a number of neutral mutations. Genetic genealogists analyze one of these neutral regions for differences, which indicate that later generations with the same mutations are related. These differences occur at the rate of about one every 20,000 years.

Out of Africa

Sykes applied the mitochondrial DNA knowledge to determine the progress of Homo sapiens out of Africa, the only place where there are fossils covering the last three million years from Homo erectus, to Homo neanderthalensis, to Homo sapiens. In 1997, DNA was sequenced from a Neaderthal and it had 26 differences from the average modern European, which indicates that they last shared a common ancestor about 250,000 years ago.

After collecting thousands of DNA samples from across Europe, Sykes fit the sequences into a scheme to show their evolutionary relationship to one another. He found seven clusters that frame the population of Europe. Six of the seven were older than ten thousand years. Historians had previously believed that agriculturalists overwhelmed the last of the hunter-gatherers on the European landscape after the last Ice Age. But the mitochondrial DNA showed otherwise. It provided evidence that most of Europe is populated by people whose ancestors endured the last Ice Age.

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