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Polymerase Chain Reaction - PCR - PowerPoint PPT Presentation


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Polymerase Chain Reaction - PCR. The polymerase chain reaction (PCR) is a technique to amplify a piece of DNA very rapidly outside of a cell. Some applications of PCR. Forensic medicine. Preimplantation Genetic Diagnosis (PGD). Archeology. Paternity testing.

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slide2
The polymerase chain reaction (PCR) is a technique to amplify a piece of DNA very rapidly outside of a cell.
some applications of pcr
Some applications of PCR.
  • Forensic medicine.
  • Preimplantation Genetic Diagnosis (PGD).
  • Archeology.
  • Paternity testing.
a cycle of pcr consists of three steps
A cycle of PCR consists of three steps.
  • DNA denaturation at 95 degrees C.
  • Primer annealing at 50-60 degrees C.
  • DNA polymerization by a thermostable DNA polymerase at 72 degrees C.
slide6
Starting with a single molecule of DNA, 25 rounds or cycles of PCR will produce about 10 million identical DNA molecules!!
forensic uses of pcr
Forensic uses of PCR
  • PCR can be used to amplify DNA from a small amount of cells (about 1000 cells).
  • The amplified DNA from cells can be used in DNA fingerprinting analysis to determine who was at the crime scene.
dna fingerprinting using pcr in forensic investigations
DNA fingerprinting using PCR in forensic investigations.
  • DNA is isolated from blood at a crime scene and amplified by PCR.
  • The amplified DNA is digested with restriction enzymes and resolved on an agarose gel.
  • Southern blot analysis is performed to give a DNA fingerprint.
individuals have unique dna fingerprints because of restriction length polymorphisms rflps
Individuals have unique DNA fingerprints because of restriction length polymorphisms (RFLPs).
how reliable is dna fingerprinting
How reliable is DNA fingerprinting?
  • DNA regions chosen are ones known to be highly variable from one person to another.
  • In most forensic cases, the probability of two people having identical DNA fingerprints is between one chance in 100,000 and one in a billion.
  • The exact number depends on the number of probes used to different regions of human chromosomal DNA.
slide13
Many argue that DNA evidence is more reliable than eyewitnesses in placing a suspect at the scene of a crime.
satellite dna can be used as markers for dna fingerprinting
Satellite DNA can be used as markers for DNA fingerprinting.
  • Satellite DNA consists of tandemly repeated base sequences within the human genome.
  • The most useful satellite DNA for forensic purposes are microsatellites having repeating units of only a few base pairs, and the number of repeats are highly variable from one person to another.
  • Microsatellite DNA is also called a simple tandem repeats (STRs).
strs in dna fingerprinting
STRs in DNA fingerprinting.
  • The greater the number of STRs analyzed in a DNA sample, the more likely the DNA fingerprint is unique to an individual.
  • PCR is used to selectively amplify particular STRs before electrophoresis.
  • PCR is especially valuable when DNA is in poor condition or available in minute quantities.
pcr use in pre implantation genetic diagnosis pgd
PCR use in Pre-implantation Genetic Diagnosis (PGD).
  • PGD is a way to determine if human embryos from in vitro fertilization have genetic defects (for example, cystic fibrosis).
  • A cell is removed from an eight cell embryo and the DNA is analyzed by PCR for genetic defects.
  • Only healthy embryos are implanted into a mother’s uterus.
  • Should this technology be used for things like gender selection?