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A consumer's guide to DNA-driven genealogy and health history time capsules

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One of the most interesting time capsules you can hand over to the next generation is a medical history of your closest relatives and what they've inherited as far as health-related trends. The reason is to give future generations of relatives a handle on what their family medical histories look like. Somebody may make a map or atlas of family medical histories from one generation to the next going back a few generations.

“The human genome is about 3 x 109 base pairs long, which would weigh about 40 pg picograms: 1 pg=10-12 grams) per genome,” reports Michael Onken, and this description appears on the science Web site of Ricky J. Sethi, MadSci.ORG Administrator at MadSci.ORG at the Washington University School of Medicine. “Human cells are diploid. For example, each contains two copies of the genome, so the nuclear DNA from a human cell would weigh about 80 pg. If we want total cellular DNA, then we need to include mitochondrial DNA (mtDNA).

“The human mitochondrial genome is about 16,000 base pairs long. There are about 10 copies of the genome per mitochondrion, and there are on the order of 1,000 mitochondria per cell. This gives us about 0.2 pg of mtDNA per human cell.

“There are on the order of 1014 cells per adult human, many of which are without nuclei, like skin cells and red blood cells. This would give us just under a kilogram of chromosomal DNA and on the order of a few grams of mitochondrial DNA in the average human body.”

(This excerpt is reprinted with permission of Ricky J. Sethi, MadSci.ORG Administrator, at the Washington University School of Medicine, according to the website. Knowing how many genes a human has in the future will help not only genealogists and other family and oral historians trace ancestors and keep records of lineages, but physicians will be able to tailor medicines to help people based on how their individual genes react to different elixirs, drugs, natural supplements, herbs, foods, and medicines.

Combined with the knowledge of rainforest tropical plants and their cures, the human genome is headed towards individualization and customization, with an appropriate mixture of food, medicine, or therapy based on one’s individual genetic makeup.

To the person without a science background, knowing one’s genes also is a way to connect people to their common ancestors in the past and to those descendants. Family history can be researched not only for medical reasons, but for historical reasons, and to show how people are related to one another down through the ages.

To understand how DNA testing relates to history and family records, let’s look at some basics of genomics such as what are cells and what is DNA. Then we can think about ways we can use the results of DNA tests in the realm of family history.

Credit for the following Primer below and Dictionary at the back of this book is acknowledged to the U.S. Department of Energy Human Genome Program as the source for both and included also here is the U.S. Department of Energy Human Genome Program’s web site for more information on the Human Genome Project and its applications.

This document may be cited in the following style: Human Genome Program, U.S. Department of Energy, Genomics and Its Impact on Medicine and Society: A 2001 Primer, 2001. For printed copies, please contact Laura Yust at Oak Ridge National Laboratory. Send questions or comments to the author, Denise K. Casey. Site on the Web designed by Marissa Mills. This primer was prepared by Denise Casey, Human Genome Management Information System, Oak Ridge National Laboratory. You can find this Primer on the Web and the index to additional publications at the Primer 2001 site. Or see, "Genomics and Its Impact on Medicine and Society: A 2001 Primer (Courtesy of the U.S. Department of Energy Human Genome Program."

The Basics

Cells are the fundamental working units of every living system. All the instructions needed to direct their activities are contained within the chemical DNA (deoxyribonucleic acid). DNA from all organisms is made up of the same chemical and physical components. The DNA sequence is the particular side-by-side arrangement of bases along the DNA strand (e.g., ATTCCGGA). This order spells out the exact instructions required to create a particular organism with its own unique traits.

The genome is an organism’s complete set of DNA. Genomes vary widely in size: the smallest known genome for a free-living organism (a bacterium) contains about 600,000 DNA base pairs, while human and mouse genomes have some 3 billion. Except for mature red blood cells, all human cells contain a complete genome.

DNA in the human genome is arranged into 24 distinct chromosomes—physically separate molecules that range in length from about 50 million to 250 million base pairs. A few types of major chromosomal abnormalities, including missing or extra copies or gross breaks and rejoinings (translocations), can be detected by microscopic examination. Most changes in DNA, however, are more subtle and require a closer analysis of the DNA molecule to find perhaps single-base differences.

Each chromosome contains many genes, the basic physical and functional units of heredity. Genes are specific sequences of bases that encode instructions on how to make proteins. Genes comprise only about 2% of the human genome; the remainder consists of noncoding regions, whose functions may include providing chromosomal structural integrity and regulating where, when, and in what quantity proteins are made. The human genome is estimated to contain 30,000 to 40,000 genes, but could contain around 70,000 genes. The exact figure is not fully agreed upon yet.

Although genes get a lot of attention, it’s the proteins that perform most life functions and even make up the majority of cellular structures. Proteins are large, complex molecules made up of smaller subunits called amino acids.

Chemical properties that distinguish the 20 different amino acids cause the protein chains to fold up into specific three-dimensional structures that define their particular functions in the cell

The constellation of all proteins in a cell is called its proteome. Unlike the relatively unchanging genome, the dynamic proteome changes from minute to minute in response to tens of thousands of intra- and extra cellular environmental signals.

A protein’s chemistry and behavior are specified by the gene sequence and by the number and identities of other proteins made in the same cell at the same time and with which it associates and reacts. Studies to explore protein structure and activities, known as proteomics, will be the focus of much research for decades to come and will help elucidate the molecular basis of health and disease.

The new interactive atlas (map) of human genetic history

An interactive map of human genetic history finally has been published. A report of the research, "A Genetic Atlas of Human Admixture History," is revealed in Science, February 13, 2014. The interactive map, produced by researchers from Oxford University and the University College London (UCL), details the histories of genetic mixing between each of the 95 populations across Europe, Africa, Asia and South America spanning the last four millennia. You can check out the admixture atlas here.

The study simultaneously identifies, dates and characterizes genetic mixing between populations. To do this, the researchers developed sophisticated statistical methods to analyze the DNA of 1490 individuals in 95 populations around the world. The work is chiefly funded by the Wellcome Trust and Royal Society.

"DNA really has the power to tell stories and uncover details of humanity's past," says Dr Simon Myers of Oxford University's Department of Statistics and Wellcome Trust Center for Human Genetics, co-senior author of the study, according to the February 13, 2014 news release, Interactive map of human genetic history revealed.

"Because our approach uses only genetic data, it provides information independent from other sources. Many of our genetic observations match historical events, and we also see evidence of previously unrecorded genetic mixing. For example, the DNA of the Tu people in modern China suggests that in around 1200CE, Europeans similar to modern Greeks mixed with an otherwise Chinese-like population. Plausibly, the source of this European-like DNA might be merchants traveling the nearby Silk Road."

The technique is called Globetrotter

The powerful technique, christened 'Globetrotter', provides insight into past events such as the genetic legacy of the Mongol Empire. Historical records suggest that the Hazara people of Pakistan are partially descended from Mongol warriors, and this study found clear evidence of Mongol DNA entering the population during the period of the Mongol Empire. Six other populations, from as far west as Turkey, showed similar evidence of genetic mixing with Mongols around the same time.

"What amazes me most is simply how well our technique works," explains Dr Garrett Hellenthal of the UCL Genetics Institute, lead author of the study, according to the news release. "Although individual mutations carry only weak signals about where a person is from, by adding information across the whole genome we can reconstruct these mixing events. Sometimes individuals sampled from nearby regions can have surprisingly different sources of mixing.

"For example, we identify distinct events happening at different times among groups sampled within Pakistan, with some inheriting DNA from sub-Saharan Africa, perhaps related to the Arab Slave Trade, others from East Asia, and yet another from ancient Europe. Nearly all our populations show mixing events, so they are very common throughout recent history and often involve people migrating over large distances."

The team used genome data for all 1490 individuals to identify 'chunks' of DNA that were shared between individuals from different populations. Populations sharing more ancestry share more chunks, and individual chunks give clues about the underlying ancestry along chromosomes

"Each population has a particular genetic 'palette'," says Dr Daniel Falush of the Max Planck Institute for Evolutionary Anthropology in Leipzig, co-senior author of the study, according to the news release. "If you were to paint the genomes of people in modern-day Maya, for example, you would use a mixed palette with colors from Spanish-like, West African and Native American DNA. This mix dates back to around 1670CE, consistent with historical accounts describing Spanish and West African people entering the Americas around that time. Though we can't directly sample DNA from the groups that mixed in the past, we can capture much of the DNA of these original groups as persisting, within a mixed palette of modern-day groups. This is a very exciting development."

As well as providing fresh insights into historical events, the new research might have implications for how DNA impacts health and disease in different populations. "Understanding well the genetic similarities and differences between human populations is key for public health,' says Dr Simon Myers, according to the news release.

"Some populations are more at risk of certain diseases than others, and drug efficacy is also known to vary significantly. Rare genetic mutations are particularly likely to show strong differences between populations, and understanding their role in our health is an area of intense current research efforts," says Dr Simon Myers, according to the news release. "We hope in future to include even more detailed sequencing, to spot these rare mutations and better understand their global spread. Our method should be even more powerful when applied to these future data sets, providing rich opportunities for future work."

The Oxford University John Fell Fund, the National Institutes of Health (USA), the Wellcome Trust, the Biotechnology and Biological Sciences Research Council and the joint Royal Society/Wellcome Trust Sir Henry Dale Fellowship funded the research. For additional information about the work and its main findings, please see the FAQ site at the genetic admixture PDF article. Also you can check out sites such as, "A genetic atlas of human admixture history " and "A genetic atlas of human admixture history."

The Wellcome Trust is a global charitable foundation dedicated to achieving extraordinary improvements in human and animal health. It supports the brightest minds in biomedical research and the medical humanities. The Trust's breadth of support includes public engagement, education and the application of research to improve health. It is independent of both political and commercial interests.



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