4.1. Genetics as a Tool in Anthropology

Transcription

1 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

2 Cells and Chromosomes Chromosome 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.

3 Human Chromosomes All biological cells contain pairs of chromosomes, of different size Human cells have 23 pairs. Chromosome DNA contains gene sequences reflecting heritage Chromosomes determine body functions a chromosome contains one DNA & protein. The two chromosomes in each pair are inherited from the each of the parents. Two of the chromosomes identify the human sex, X, Y

4 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

5 Genes Genes are small sections of DNA structure which are built by sequences of molecule building blocks Adenine Cytosine Guanine Thymine A C G T Individual genes come with small variations in the sequences of the four building blocks which are mounted in between a phosphate deoxyribose structure.

6 Basic DNA structure Genetics 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.

7 DNA Structure Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid J. D. WATSON, F. H. C. CRICK CONTEXT: 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

8 Fluorescence Techniques Important technique is to mark gene molecules by dye which can be visualized by fluorescence of light or laser light of selected frequencies. Lung cell, DNA is stained in blue and cytoplasma of cell in green. 24 dyed Chromosomes! Each chromosome is labeled in characteristic color

9 DNA Sequencing Techniques 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. 50 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 Mb.

10 Sequencing Markers 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

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

12 Three types of DNA... X & Y chromosome 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 Mitochondrial DNA & the Y chromosome DNA sequencing provides new key for Anthropology!

13 Population Genetics Statistical 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. Polymorphism means that genes differ by more than 1 allele in their sequence. The assumption is that mutation occurs statistically at a constant rate with time.

14 Genetic Markers 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! R STR 1 500generations 25R STR 1 20generations y Single Nucleotide Polymorphism SNP: GAATCAT mutates to GAATTAT R SNP 6 10 SNP SNP 1generation 10 SNP y / y

15 Genetic Distances Genetic distances are statistical units to determine the genetic differences between populations. d = 2 ( ) 2 x y P ( 1 P) d: frequency correlation x: frequency for one allele in population 1 y: frequency for one allele in population 2 P: mean gene frequency for all populations Correlation with evolutionary time: t t 1 2N d = e D = log 1 ( d ) = t 2N N: effective population size D: genetic distance

16 Genetics and Language