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DNA Research and Genealogy

DNA Factsheet:

A. About DNA
B. DNA race and blood groups.
C. Mitochondrial DNA
D. DNA and Sex
E. DNA and Human History
    Earliest Humans
    The last 12,000 years
F. DNA and genealogy research

DNA Testing
Bibliography

A. About DNA

  • Genetics
    • Study of inheritance
    • Gregor Mendel laid the foundation of the study in 1860s.
    • Mendel concluded that whatever was determined by heredity was inherited equally from both sets of parents.
      • There are two important exceptions: the "Y" Chromosome and the mDNA
  • Chromosomes
    • Their role in genetics was understood in 1903
    • So called because they become brightly coloured with certain dyes developed to enhance them under the microscope.
    • Made of DNA: Deoxyribonucleicacid.
    • Double helix structure was discovered in 1953 by James D. Watson and Francis Crick.
    • Made up of four nucleotide bases
      • Adenine
      • Cytosine
      • Guanine
      • Thymine
    • Human beings have 46 chromosomes arranged in pairs with the important exception of the female "X" and male "Y" chromosome.
      • Female egg always contains an X chromosome.
      • Male sperm may contain an X or Y chromosome, and this decides the gender of the offspring.
    • Basic unit is the gene
    • The basic mechanism by which they work is the manufacture proteins.

B. DNA, Race and blood groups

  • Race
    • In the 19th century scientists divided human beings into races.
    • The racial characteristics may be very visibly obvious, but DNA research reveals that the genetic differences between the races are relatively small. Hair colour and skin colour and such characteristics are very minor genetic differences.
    • The genetic evidence is that races are very recent developments, and that all modern humans came out of  Africa in the last 150,000 years, and not the product of multi-regional development as had been previously thought.
    • More usefully the major genetic groupings of human beings are blood groups.
  • Blood Groups
    • Are complex factors, however most crucially certain broad groupings are commonly described because these are most important for blood transfusions: O, A, B, AB,
      • O, is the oldest and most common amongst people of African origin.
      • B, is the second oldest, most common in East Eurasia.
      • A, third on the scene, most common in Europeans
      • AB, most recent, most common in Eastern Europe because it represents the mixing of Western and Eastern.
      • Rhesus is a separate grouping from the ABO system. Because of the antagonism between the Rhesus positive and Rhesus negative the older Rhesus negative has largely died out, apart from in Europe where the older Rhesus negative and newer Rhesus positive populations mixed in comparatively more recent times (8,000 years).
    • Blood groups have been used to trace the movement of humans from Africa to Eurasia and beyond. DNA research has enabled a more in-depth understanding of this process.

C. Mitochondrial DNA

  • What Mitochondria are
    • Energy production centre of the cell.
    • Contain Adenosine Tri Phospate ATP.
    • Believed to be a result of a symbiotic relationship of two original organizms that eventualy merged to form the cell as we know it.
  • Mitochondrial DNA
    • Because of their history as an individual organism the mitochondria contain a vestige of their own DNA called mDNA.
    • mDNA is only passed down from mother to children because it is only present in the egg. The small amount present in the mitochondria of the sperm to enable it to swim is destroyed during fertilization.

D. DNA and Sex

  • When a cell reproduces itself by division it produces two identical copies of itself. This is called meitosis.
  • In sexual reproduction the cell produces a copy with only half of it DNA pairs. This is called meiosis.
  • Sexual reproduction is very inneficient, but brings an enormous advantage in confering individuality on the offspring and consequently resistance to parasites.
  • In humans this has led to one chromosome the "Y" that decides the sex of the offspring, but does not join in the pairing and recombination that takes place with the other chromosomes.

E. DNA and Human History

·         The First Humans

    • Most of these stages of human evolution occured in East Africa.
    • They did not occur in a straight line. There were probably several species of humans that did not make it.
      • About 6 million years ago a population of African apes split into two species. One led to modern humans and the other to chimpanzees.
      • More than 4 million years ago one of the species that was to become humans began to spend most of its time on 2 legs. This has come to be called Austrolpithecus.
        • The customary explanation of this change is usualy given in terms of the decrease in forest, leading to the move of apes onto open savannah.
        • There is an alternative explanation called the aquatic ape theory. This suggests that a group of primates were actually moving toward returning to the ocean, much as did the ancestors of other aquatic mammals.
      • Around 2 million years ago a species of large and particularly brainy bipeds began to use tools. This is given the name Homo.
      • 100,000 to 200,000 years ago a new group appeared within the genus Homo. This is the group from which we are all descended.
      • Somewhere around 150,000 years ago their may have been 20,000 humans, from one female of these all the 6 billion people alive today are descended in about 7,500 generations. It has also been estimated that all people alive today share the DNA of about 86,000 people

·         The last 12,000 years

    • Up to 12,000 years ago humans has lived a hunter gatherer existence.
    • 12,000 years ago agriculture began in the middle east.
    • 10,000 years ago towns develop - e.g. Jericho, "the worlds oldest town". Actually there were a number of simmilar ones in the region.

E. DNA and Genealogy Research

  • Because "Y" Chromosomes and mDNA are not part of the recombination process they are copied almost exactly from parent to child.
  • Mutations are errors that occur in this process over time.
  • Mutations can be tracked over a period of time and the relative distance between people geneticaly speaking, and from common ancestors can be ascertained.
  • There are thus basicaly two types of DNA research of genealogical interest.
    • "Y" chromosome research. The Y chromosome is passed only from the father and so is generaly found useful in the traditional genealogy that is based upon the patrilinear line. It can be used to:
      • Show if two people, or more, have a common ancestor.
      • Geographic origins.
      • Native American, Asian, African origins.
    • mDNA research. The mDNA mutates very slowly and so over the whole span of human history 43 broad "clans" (including 7 European ones) have been identified all going back to one woman labeled "mitochondrial Eve" who lived about 150,000 years ago.
      • Geographic origins
      • Native American, Asian, African origins.

DNA Testing:

There are a number of organizations that offer DNA testing kits.

Oxford Ancestors

Ancestry By DNA

Family Tree DNA

Bibliography

Olson, Steve; Mapping Human History: Genes Race and Our Common Origins. Mariner Books; Boston, NY.

Sykes, Bryan; Adam's Curse: A Future Without Men. W.W.Norton&Co., New York, London.

Sykes, Bryan; The Seven Daughters of Eve: The Science That Reveals our Genetic Ancestry. W.W.Norton&Co, New York, London.

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