tag:blogger.com,1999:blog-49704279093369607132012-02-16T19:33:17.473-08:00CSInoreply@blogger.comBlogger301100tag:blogger.com,1999:blog-4970427909336960713.post-85843082682688354962011-05-17T20:51:00.000-07:002011-05-17T20:51:01.088-07:00

Any biological fluid or tissue that contains nucleated cells can be used as a source of DNA. A nucleated cell is any cell that has a nucleus. In blood the white blood cells have nuclei and therefore have DNA, but the red blood cells do not. The sperm cells contain most of the DNA that is in semen, but there are also some epithelial cells, which contain DNA. Much less DNA is obtained from a

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-28074383961936555572011-05-17T20:48:00.000-07:002011-05-17T20:48:22.017-07:00

Suppose a scientist were looking for a certain sequence pattern in a mixture of DNA fragments of different sizes. The mixture could be separated by electrophoresis on an agarose gel and then fixed on a membrane by Southern blotting. Then, in order to locate the desired DNA sequence pattern on the blot, a single-stranded segment of DNA called a “probe” could be added directly to the blot. A probe

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-40238966579187553492011-04-26T19:09:00.000-07:002011-04-26T19:09:00.297-07:00

As DNA analysis methods were being developed, it was common to separate DNA fragments of different sizes on agarose gels, as described in the preceding section. Many times, though, scientists wanted to do further testing steps that just would not work in gels. A biochemist named Edwin Southern came up with a method to solve this problem in 1975. Southern’s method employs a membrane made of

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-91422869287988518852011-04-25T19:06:00.000-07:002011-04-25T19:06:00.394-07:00

Scientists often need to see whether DNA was successfully prepared from cells or tissues in evidence, how big the molecules are, and how much DNA is in the preparation. Gel methods are commonly used for these purposes. Gel methods provide a way of visualizing DNA. DNA is a very large molecule that is highly negatively charged. As a result it can be moved by electrophoresis in a gel medium.

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-36341669177874435972011-04-24T19:05:00.000-07:002011-04-24T19:05:00.646-07:00

Restriction enzymes were important in the RFLP forensic DNA-typing procedure. Many different bacteria make special enzymes called restriction endonucleases, or restriction enzymes. There are many different restriction enzymes, but they all do one thing: They cut the doublestranded DNA molecule at a specific place. Strictly speaking, the enzyme itself does not “cut” DNA; it catalyzes the

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-59561972472796935922011-04-23T19:03:00.000-07:002011-04-23T19:03:00.844-07:00

Because mitochondria have their own DNA, separate from nuclear DNA, one can speak of a “mitochondrial genome,” all the DNA contained in a mitochondrion. Cells have many mitochondria, so there are multiple copies of mtDNA in every cell. The MtDNA genome is significantly smaller than the nuclear genome. The nucleus has about 3.5 billion base pairs in its DNA; the mitochondrion has about 16,500 base

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-28604732076957743642011-04-22T19:00:00.000-07:002011-04-22T19:00:01.628-07:00

The DNA discussed so far is found in the nucleus of the cell, in the chromosomes. In addition to this nuclear DNA, cells also contain DNA in small structures outside the nucleus called “mitochondria.” The accompanying diagram of a generalized animal cell shows the nucleus and mitochondria, as well as the other cell structures. Mitochondria contain the cell’s energy-processing machinery, but they

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-31163502396808817172011-04-21T18:58:00.000-07:002011-04-21T18:58:00.737-07:00

The regions of DNA that forensic scientists use to individualize people contain repeated sequences. There are different types of repeat-sequence DNA. A repeated sequence may be found in many different places in the genome. These can be called “interspersed” sequences. Some repeated sequences are head-to-tail repeats of a sequence altogether at one location within the DNA. These are sometimes

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-45057738310853667662011-04-20T18:51:00.000-07:002011-04-20T18:51:00.332-07:00

It is often remarked that no two people except identical twins have the same DNA. As far as scientists now know, the statement is true, but like many generalizations, it hides a lot of the detail. What the human genome project has shown is that about 20 percent of human DNA actually specifies protein structure. Much of the DNA that specifies protein structure is pretty similar among different

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-70709819783995888132011-04-19T18:45:00.000-07:002011-04-19T18:45:00.839-07:00

The original DNA-typing method, the one Jeffreys used in the Narborough case, was too cumbersome and time consuming to be useful for casework and database construction. A different, faster technology was needed. It was developed in 1985. The polymerase chain reaction is one of the most stunning breakthroughs in all DNA science. The idea is attributable to Kary Mullis, who worked for Cetus

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-24414799536120814782011-04-18T18:40:00.000-07:002011-04-18T18:40:00.539-07:00

In 1983, in England, a 15-year-old girl who was walking home along a country lane near Enderby became the victim of rape and murder. The investigation yielded no suspects. Three years later another young girl was sexually assaulted and murdered in a similar manner in the nearby village of Narborough. Police arrested a teenager named Rodney Buckland, who worked in a local mental hospital. Buckland

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-13808354011719072472011-04-17T18:38:00.000-07:002011-04-17T18:38:00.509-07:00

Starting in the 1980s, methods were developed that made DNA sequencing much easier and faster than it had been. These methods could be automated, enabling a very large amount of sequence data to be collected in many laboratories throughout the world. With these methodologies in place in the larger research centers, the U.S. government and a private company made commitments to pursue sequencing

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-53996031561641272842011-04-16T18:24:00.000-07:002011-04-16T18:24:00.775-07:00

In 1944 Oswald T. Avery, Colin M. MacLeod, and Maclyn McCarty of the Rockefeller Institute in New York published a paper in the Journal of Experimental Medicine that was to become a classic. Scientists had suspected for some time that DNA was the genetic material, but it had not been experimentally established unequivocally. The question was, Is it really DNA that carries information from one

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-38432768477392143482011-04-15T18:22:00.000-07:002011-04-15T18:22:00.266-07:00

As the Avery-MacLeod-McCarty experiments in the 1940s showed, DNA specifies the cell’s activities. It was now clear that DNA directs the course of cell development and differentiation in multicellular animals, thus forming the individual. It then has a role in maintaining life functions, in repair of damaged cells or tissues, in healing, and in fighting off disease. But scientists did not yet

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-30115815892787875252011-04-14T18:17:00.000-07:002011-04-14T18:17:01.028-07:00

Around 1900 the study of genetics really took off. One pioneering group was that of the noted biologist Thomas Hunt Morgan, a faculty member of Columbia University in New York City. Around this time the fruit fly, Drosophila melanogaster, became the geneticist’s research animal of choice. These little flies have many characteristics that are easy to observe under a magnifier or a low-power

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-3627607256896256422011-04-13T18:15:00.000-07:002011-04-13T18:15:00.407-07:00

The earliest known systematic experiments in genetics were performed by an Augustinian monk named Gregor Mendel (1823–84). Although his work was presented and recorded in a scientific proceeding in 1865, not many people heard about it until more than three decades later. The scientific society and its proceedings, where the work was originally described, were obscure, and no one in mainstream

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-6900940910672652282011-04-12T18:07:00.000-07:002011-04-12T18:07:00.208-07:00

In a suburban community near a large city a woman was violently assaulted in her home. She had arrived home and surprised a burglar. She fought with the intruder briefly and received injuries, from blows and from being cut with a knife. She did not get a very good look at the perpetrator. There had been a series of burglaries in the area, and police had some information from other victims that

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-9615117029907437402011-04-10T17:59:00.000-07:002011-04-10T17:59:00.343-07:00

Let us call the people involved in this case Jane Doe and John Smith. Who they are is not important to understanding the scientific issues. In the 1980s Jane Doe reported a sexual assault in a suburban town adjacent to New York City. The clinical examination she underwent at the time included taking a vaginal swab, among other items, into evidence. Doe was a type B secretor, so she would produce

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-5058100981461824882011-04-09T17:50:00.000-07:002011-04-09T17:50:00.388-07:00

In the late 1970s a woman named Cathleen Crowell-Webb reported a sexual assault in a suburb of Chicago. At the time the case was “routine”; that is, it did not differ from any of the hundreds of such cases that come into forensic laboratories every year. Crowell was found to be a type B secretor, and the suspect in the assault, Gary Dotson, was also a type B secretor The physical evidence in the

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-54841308491675390802011-04-08T17:40:00.000-07:002011-04-08T17:40:00.483-07:00

In 1916 Dr. Leone Lattes published two cases that illustrated the forensic value of the then new technique for ABO typing bloodstains. Lattes used a method for determining the ABO type of bloodstains that relied on detection of the specific antibodies. Although published 15 years after Landsteiner first described the ABO blood group system in human beings, this work is the first report of ABO

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-62563191158801011422011-04-07T17:36:00.000-07:002011-04-07T17:36:00.142-07:00

In May 1992 the body of a woman later identified as Denise Johnson was found outdoors in the brush near some paloverde trees in Maricopa County, Arizona. Her clothing was scattered about the area, and she had been bound with cloth and braided wire. She was from nearby Phoenix and appeared to have been murdered and left at the location recently. A pager recovered at the scene led the police to a

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-47205759496891927142011-04-06T17:34:00.000-07:002011-04-06T17:34:00.201-07:00

There are at least two different ways plant materials can be useful as forensic evidence. One way—perhaps the most obvious—is as “trace” materials. Trace evidence can be many things, including hairs, fibers, glass, soil, and cosmetics, as well as plant materials that might consist of leaves, stems, flowers, seed pods, tree bark, or pollen. Many plants reproduce by producing pollen or spores,

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-20252513239614127992011-04-05T17:30:00.000-07:002011-04-05T17:30:01.000-07:00

Entomology is the study of insects; forensic entomology is the study of insects to help resolve legal questions. One of the most important uses of forensic entomology is to help uncover information about certain human deaths. There are more species (different kinds) of insects than any other group of plants or animals on Earth. They make up nearly 25 percent of all the known living organisms.

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-55877862812556995302011-04-03T17:28:00.000-07:002011-04-03T17:28:00.199-07:00

The interpretation of blood patterns is the reconstruction aspect of forensic blood analysis. It is distinct from identification, species testing, and DNA analysis. During violent events blood can drip from a source, or it can be spattered onto floors, walls, and objects. The patterns the blood forms on the surfaces can help a forensic scientist know what type of event caused the blood to spatter

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-33492165540333971352011-04-02T17:26:00.000-07:002011-04-02T17:26:00.405-07:00

Most societies consider it important to recognize the death of an individual and to dispose of his or her remains in a particular way. Most people die under circumstances where their identity is not in question. But in cases where deaths are sudden or unexpected, occur without any medical oversight (outside a clinic or hospital), or might involve foul play, they are investigated by medical

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-8366177119868599022011-04-01T17:24:00.000-07:002011-04-01T17:24:00.541-07:00

Not too long after the discovery of blood types, it became clear that they were inherited. The ability to test for discrete, inherited characteristics opened the way to using genetic testing as a means of trying to establish (or disprove) parentage. A child’s mother is usually known because there is some record of the child being born to her, so most disputed parentage cases involve disputed

CSInoreply@blogger.com0tag:blogger.com,1999:blog-4970427909336960713.post-78267808018338464842011-03-30T19:04:00.001-07:002011-03-30T19:05:14.754-07:00

Forensic DNA typing was made possible not only by advances in knowledge about DNA structure and function but also by advances in the methods and techniques allowing DNA to be manipulated. Different manipulation methods apply to different DNA-typing technologies. For example, nuclear DNA was first typed using the restriction fragment length polymorphism (RFLP) technique. This procedure did not

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-45828307408042309072011-03-30T18:38:00.000-07:002011-03-30T18:38:16.991-07:00

In the 1980s DNA scientists (molecular geneticists) focused on the repeat-sequence polymorphism within DNA. For most researchers these repeat-sequence regions were “road signs” along the sequence of letters (bases) as different laboratories worked on sequencing the entire human DNA. Dr. Alec Jeffreys at the University of Leicester in the United Kingdom realized that these polymorphisms provided

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-35327040892224541462011-03-30T18:37:00.000-07:002011-03-30T18:37:59.054-07:00

Much of the repeated sequence data in the human genome is not functional; it does not specify protein structure. It has been called “junk DNA,” though it may have functions that are not yet clear to scientists. About 20 percent of human DNA is functional, in the sense that it codes for protein. And, within that 20 percent, there is considerable similarity in sequence among different people. This

CSInoreply@blogger.comtag:blogger.com,1999:blog-4970427909336960713.post-73932829560998546602011-03-30T17:23:00.000-07:002011-03-30T17:23:20.365-07:00

Once established as human, blood and physiological fluid stains and traces are next DNA typed to find out who may have deposited them. DNA profiling means finding out the DNA types at several different genetic loci. Genetic loci, or different locations on the DNA, are explained later in the book. The combined set of types at the different locations is the profile. It is the profile that is

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