Forensic Science Chapter 1 Summary

Pre-Reading Notes (Very Short Introduction - Chapter 5; Fundamentals of Forensic Science – Chapter 11):
• Red and white cell blood antigens are polymorphic: they exist in more than one form and everyone inherits one or more forms of each of them
• A successful DNA profile makes it possible to reach a conclusion that a DNA sample came from a specific individual, giving law enforcement and forensic science a new, powerful identification tool that complements fingerprints and other methods of identification
• DNA (deoxyribonucleic acid) – found in nearly all cells expect nerve cells and dead red blood cells
• DNA is a polymer – a molecule made up of repeating simpler units called monomers
• DNA located in the nucleus and in the mitochondria
• Described
as a double helix. The poles of the ladder are identical in all living things. They are made up of alternating sugar molecules (deoxyribose) and phosphates. Dangling off each sugar molecule is one of four vases (nucleotides): Adenine (A), guanine (G), cytosine (C), and thymine (T). A goes with T and C goes with G. Order of pairs controlled by genetics; order of the base pairs contains a genetic code that determines many of the characteristics of a person.
• Most DNA found in the nucleus. Nucleus is where most of the cell function are controlled and is arranges into 46 structures called chromosomes. The chromosomes are arranged in 23 pairs. One member of each pair of chromosomes comes from the father and the other from the mother. One pair of chromosomes determines the sex of the individual. For females, chromosomes are the X types; for males, one is X and the other is Y.
• Genes provide the chemical instruction to manufacture particular proteins in the body. These genetic instructions are copied onto RNA (ribonucleic acid), which transmits this information to protein manufacturing sites in the cell. Each gene codes for a particular characteristic protein like hair colour, eye colour, and skin pigmentation. 99% of all human DNA is exactly the same; less than 1% contains the genetic information that differentiates on human being from another.
• Two different (e.g.
eye colour) genes are called alleles. If a person inherits the same form of a gene from the mother and the father, that person is said to be homozygous. If a person inherits two different forms of the same gene, they are said to be heterozygous. Some alleles are dominant, whereas others are recessive – dominant are the genes you will display if you get two different types of genes.
• The variation of alleles at several loci can be combined to provide a statistical evaluation of the likelihood of a particular set of alleles in a given population
• Visible manifestation of variability (eye colour, hair colour) is called the phenotype
• The genotype is the genetic description of the allele
• In DNA analysis, locations (loci) that are polymorphic are purposely chosen. These loci exhibit variation among members of a population. The more variation there is at a locus, the more discriminating the analysis will be
• Two types of variability in alleles. The first type is sequence polymorphisms. The other type of variation in DNA is called length polymorphism (repetition – tandem repeats) When variation in the number of repeats occurs from one individual to the next, then this locus is described as having a variable number of tandem repeats (VNTR). A person’s DNA type is a description of the types of alleles at all of the locations being analysed on the
genome