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DNA Biochemical Processes and Forensic Applications. 1.

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Presentation on theme: "DNA Biochemical Processes and Forensic Applications. 1."— Presentation transcript:

1 DNA Biochemical Processes and Forensic Applications. 1

2 Revision of DNA 2

3 Biochemical Processes Sequences of nucleotides code for specific traits/characteristics These individual traits are at the same position on a chromosome in everyone (unless a large mutation has occurred) The different traits for a specific gene are called alleles – e.g. Blue, green and brown eyes are different alleles for eye colour. 3

4 Biochemical Processes (cont.) It is alterations to these alleles that are most often the cause of genetic diseases DNA structure/sequence determines protein structure Proteins are determined by the sequence of amino acids Amino acids are determined by the sequence of bases (also called codons or triplet codes) Changing just one of these bases in a codon can change what amino acid is produced 4

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6 Genes and Inheritance A normal persons genome contains two of each of the 22 chromosomes as well as a pair of sex chromosomes which will be either XX of XY Your genes are a combination of your parents genes Their gametes contain half of their genome Many genetic traits are referred to as either dominant or recessive 6

7 Genes and Inheritance (cont.) Recessive trait – a person needs to have the gene on both of the chromosomes to express the characteristic Dominant trait – a person requires only one copy of the gene to express the characteristic 7

8 Sickle Cell Anaemia Affects the haemoglobin Most common form is caused by a recessive trait on chromosome 11, a single base change (T A) which makes the 6 th codon Val not Glu on the β-globin polypeptide Causes RBCs to form a sickle shape when the concentration of oxygen is low 8

9 Sickle Cell Anaemia (cont.) 9

10 This occurs most often near active tissues as they produce more energy The shape of the RBCs causes clots to form more easily in narrow blood vessels due their shape Once the RBC has formed the sickle shape its lifespan is greatly reduced 10

11 Cystic Fibrosis A recessive disease Caused by the omission of one amino acid (Phe) on chromosome 7 Protein that is coded for by this gene is responsible for the transport of Cl - across the cell membrane Defect alters the conformation of the protein so that it folds incorrectly 11

12 Cystic Fibrosis (cont.) An effected person is unable to effectively remove Cl - from the lungs, intestines, pancreas and sweat glands Sufferers also prone to lung infections and impaired digestion 12

13 Other Genetic Disorders Monosomy – where a person has only one copy of a chromosome – e.g. Turners syndrome – only one X chromosome, leads to sterility, poor health and often mental impairment Trisomy – When a person has 3 copies of a chromosome – e.g. Downs syndrome, causes physical deformities and mental impairment 13

14 Other Genetic Disorders (cont.) Trinucleotide repeat mutation – occurs when an amino acid is repeated too many times – e.g. Fragile X syndrome – repeat of CGG, a normal person has 29-31 repeats, 31-55 repeats are debateable as to if it is normal or not, 55-200 repeats are termed pre-mutation (will most likely pass it on to next generation), 200+ is full mutation causing physical mental and emotional disability the severity of which increases with the number of repeats present. – Most children with excessive repetition die before they reach adulthood. 14

15 Forensic Applications Sample selection – Need to have the samples you are testing and samples that you want to compare them with e.g blood, tissue, hair, fluid Restriction Enzymes – Target specific sequences of DNA (often a stop codon or a repeated sequence of amino acids) – Cut the chromosome into fragments which can then be analysed by their mass and electronegativity 15

16 Polymerase Chain Reaction (PCR) DNA produces an identical daughter strand every time it replicates PCR enhances this characteristic so that there is enough DNA to perform multiple analyses As little as 1 nanogram of material is needed at the beginning of this process PCR produces copies of DNA exponentially with each cycle 16

17 PCR (cont.) 17

18 Electrophoresis 18

19 Electrophoresis (cont.) 19

20 DNA Profiling 20 Approximately 5% of your DNA codes for proteins The other ~ 95% is non-coding or junk DNA which varies greatly between individuals In this junk there are sections which have repeated patterns These repeated patterns are what is used to identify an individual when doing DNA profiling a match of 10 sites across multiple chromosomes are required for positive identification

21 DNA Profiling (cont.) This information can be used for paternity, suspect identification and clearing, identification of remains, identification of species of animals, etc The exception to these rules is that it is not possible to tell the difference between identical twins as they have the exact same DNA (unless it is mutated by an external source) 21

22 Electrophoresis plate 22

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