Investigating CSI – Background material Table of Contents I ...

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Y-Chromosome Analysis (Y-STR Haplotypes) Y-chromosome haplotypes are used to uniquely identify men. Except for two small regions in which pairing and exchange take place with the X chromosome, the Y-chromosome is not subject to recombination and is passed on through the male line of the family largely unchanged. This allows a common paternal link to be traced in their ancestral lineage. By looking at Y-chromosome markers from all of the males with the same paternal descent we would suspect that all related males should share the same Y-chromosome markers. Therefore, identical Y STR patterns indicate inclusion within a family, whereas different Y STR patterns indicate familial exclusion. The figure below shows how the Y-chromosome (black squares) is passed from father to son exclusively. Testing Methodology Synergene utilises the PowerPlex Y STR kit (Promega), which allows analysis of 12 Y STR loci. Results from this analysis are compared to a population Y haplotype database. Indications for Y STR Analysis • To determine if males are from the same paternal lineage • To determine relatedness from father’s side of the family • To reconstruct family paternal-linked relationships • In sexual Assault cases, to distinguish the male sample from mixed samples: Source: www.synergeneprofiling.com 58
III. Interesting Cases Using DNA Evidence Snowball the Cat The elusive cat—both revered and demonized throughout the course of human history—has become one of the animals most important to helping scientists understand human genetics. Marilyn Menotti-Raymond is among a group of scientists studying and developing a map of the cat genome at the National Cancer Institute’s internationally renowned Laboratory of Genomic Diversity (LGD) in Frederick, Maryland. Part of the National Institutes of Health, it is the only research laboratory in the world attempting this work. “We are a cat genome center,” Menotti-Raymond says. “We have 15 researchers working on many aspects of the cat genome, from constructing genetic maps of the cat to research in natural populations of exotic felids.” It turns out that cats and humans have much in common in terms of how their genes are ordered and organized, Menotti-Raymond says. Cats have 19 pairs of chromosomes, including one pair of sex chromosomes; humans have 23 pairs of chromosomes, including one pair of sex chromosomes. “If you align human and cat chromosomes, the gene order and organization are more alike than with any other mammalian species whose genomes have been examined, except for some of the primate species,” she says. Because of the similarities, scientists believe it will be easier to identify hereditary diseases caused by defects in genes that are analogous to both cats and humans. In doing so, researchers hope to establish the cat as a useful model to further the understanding of some 200 human hereditary diseases; tumorous conditions called neoplasia; genetic factors related to infectious diseases; and mammalian genome evolution. At LGD, Menotti-Raymond is a staff scientist in the animal genetics group, where she works with five other researchers and several graduate students and postdoctoral fellows. “The work can sometimes be frustrating,” she says. “You have to like the process and be satisfied with the pursuit of knowledge.” Menotti-Raymond’s career took an unusual turn when a cat became a key part of a murder case on Prince Edward Island, Canada. In 1994, Shirley Duguay, a 32-year-old mother of five, disappeared. Her body was found in a shallow grave a few months later. Among the chief suspects in the murder was the woman’s estranged common-law husband, Douglas Beamish, who was living nearby in his parents’ home. Royal Canadian Mounted Police had no evidence linking Beamish to the crime. During the search for the victim’s body, however, the Mounties discovered a plastic bag containing a leather jacket with blood stains that matched the victim’s blood. The jacket also contained 27 strands of white hair, which forensic investigators determined were from a cat. The Mounties remembered a white cat named Snowball living in Beamish’s parents’ home. The trick was to prove the cat hair found in the jacket was Snowball’s. A Mountie investigator used the Internet to search for an expert in cat genomes, which led him to Menotti-Raymond and LGD director Stephen J. O’Brien. “They wanted to know if we could do a DNA fingerprint of the cat hair,” Menotti- Raymond says. “We had the genetic tools to do it, but it became a question of 59
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Investigating CSI - Background mate
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Page 11 and 12: Matching DNA Proving that a suspect
Page 13 and 14: Creating a DNA Profile: The Basics
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