4.1. Genetics as a Tool in Anthropology

Each biological system and every human being is defined by its genetic material. The genetic material is stored in the cells of the body, mainly in the nucleus of the cells. The cells control the operation of body functions and the reproduction of the genetic information through the generations. That means that this information can be traced to explore the origin of man.

Mitochondria

Cell nucleus

DNA distributed in Chromosomes

Cells and ChromosomesChromosome contains a section of DNA which contains many genes and proteins. The DNA section may contain up to one million nucleotides.

Cells are the building blocks of all living things; cells also contain all the hereditary information, which is passed on by cell division and DNA copying.

Human ChromosomesAll biological cells contain pairs of chromosomes, of different size

Human cells have 23 pairs.

Two of the chromosomes identify the human sex, X, Y

Chromosomes determine body functions a chromosome contains one DNA & protein. The two chromosomes in each pair are inherited from the each of the parents.

Chromosome DNA contains gene sequences reflecting heritage

Visualization by neutron crystallography

Chromosome

Neutron diffraction pattern on the molecular sample is translated into a 3 d image.

DNA molecule wrapped around a protein core

GenesGenes are small sections of DNA structure which are built by sequences of molecule building blocks

Adenine ACytosine CGuanine GThymine T

Individual genes come with small variations in the sequences of the four building blocks which are mounted in between a phosphate deoxyribose structure.

Basic DNA structureGenetics is the science of heredity and variation in biological systems! It is based on the gradual change of the gene structure in the DNA Deoxyribonucleic acid, which contains the genetic code & instructions for the biological system in the sequence of the four A, S, G, T types of nucleotides

The DNA forms a double stranded molecule, the double helix. Pair coupling of two nucleotides on the opposite strand :

A with T,G with C.

DNA StructureMolecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid J. D. WATSON, F. H. C. CRICKCONTEXT: WE wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). This structure has novel features which are of considerable biological interest. A structure for nucleic acid has already been proposed by Pauling and... Nature 171, 737 (1953)

Structure based on X-ray diffraction pattern analysis of molecule

Fluorescence TechniquesImportant technique is to mark gene molecules by dye which can be visualized by fluorescence of light or laser light of selected frequencies.

24 dyed Chromosomes!Each chromosome is labeled in characteristic color

Lung cell, DNA is stained in blue and cytoplasmaof cell in green.

DNA Sequencing Techniques

Ultimate goal is the mapping of the human Genom – the entire information distributed over the 24 chromosomes (22 autosomes, 2 sex chromosomes), with about 3 billion base pairs (A-T, C-G). Each human chromosome contains about 100-300 Mb.

50

Based on biochemical copying and multiplying methods DNA can be deciphered by sequencing techniques which determine the actual order of the DNA base A,C,G, and T that make up the gene.

Each base is tagged with different colored dye, A (green), G (yellow), C (blue), T (red). Electric field (gel electrophoresis) separates dyes forming colored bands. Laser light causes fluorescence when dye passes triggering a signal in color sensitive detector

Sequencing Markers

T G T T C G T C etc.

Sequencing Counting

Since base form always fixed pairs A-T, C-G, it is sufficient to count along one strand of DNA helix only

Three types of DNA ...

Nuclear DNA (blue print of body structure...) inherited by cell division from parents

Y chromosome DNA (determines the male sex) inherited from father to son (male XY chromosome, female XX chromosome)

Mitochondrial DNA (outside the cell nucleus) inherited from mother to children

X & Y chromosome

Mitochondrial DNA & the Y chromosome DNA sequencing provides new key for Anthropology!

Population GeneticsStatistical approach to link changes in gene structure to history of a population

Gene structure can change randomly during replication or by chemical or radiation impact. The causes a change in base sequence ⇒ Mutation. Mutation can be a replacement of a base or base addition/deletion. Only a mutation in cells associated with reproduction is transmitted to the descendants. The mutated gene is called allele and is passed on to descending generation.

The assumption is that mutation occurs statistically at a constant rate with time.

Polymorphism means that genes differ by more than 1 allele in their sequence.

Genetic Markers

ysgenerationR

sgenerationR

STR

STR

5001

20125

5001

≈≈

≈

Genetic Markers are used to map mutation rate and provide time scale.

Short Tandem Repeats - or STRs: e.g. GATA GATA GATA mutation may add or delete one of the stutters. Good for genealogy research!

Single Nucleotide Polymorphism – SNP: GAATCAT mutates to GAATTAT

ySNP

ySNPgeneration

SNPRSNP

00040010

/105.21

10 56

≡

⋅≈≈ −−

Genetic Distances

( )( )PP

yxd−⋅

−=

12

2 d: frequency correlationx: frequency for one allele in population 1y: frequency for one allele in population 2P: mean gene frequency for all populations

Genetic distances are statistical units to determine the geneticdifferences between populations.

Correlation with evolutionary time: t

( )NtdD

ed Nt

21log

1 2

=−−=

−=−

N: effective population sizeD: genetic distance

Genetics and Language