A. About DNA
B. DNA race and blood groups.
C. Mitochondrial DNA
D. DNA and Sex
E. DNA and Human History
The last 12,000 years
F. DNA and genealogy research
- 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
- There are two important exceptions:
the "Y" Chromosome and the mDNA
- Their role in genetics was understood
- So called because they become brightly
coloured with certain dyes developed to enhance them under
- Made of DNA: Deoxyribonucleicacid.
- Double helix structure was discovered
in 1953 by James D. Watson and Francis Crick.
- Made up of four nucleotide bases
- 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
- 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
- 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
- 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
- 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,
- 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
- AB, most recent, most common in
Eastern Europe because it represents the mixing of Western
- 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
- 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
- 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
- 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
- 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.
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
- 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
- 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
- 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
There are a number of organizations
that offer DNA testing kits.
Olson, Steve; Mapping Human
History: Genes Race and Our Common Origins. Mariner Books; Boston,
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.