6.3.3: DNA profiling Flashcards
What are tandem repeat sequences?
-Repetitive segments of DNA that do not code for proteins.
In 1974, when Alec Jeffreys analysed DNA from his lab technician and her parents, what did he find?
- The number of tandem repeats showed a family resemblance, but the DNA profile for each family member was unique
- He realised that a person’s DNA profile could confirm or refute paternity and maternity
What are the 6 steps in DNA profiling?
Step 1:
- DNA is obtained from the individual- either by mouth swab, from saliva on a toothbrush, from blood or hair or bones.
What are the 6 steps in DNA profiling?
Step 1: DNA is obtained from the individual- either by mouth swab, from saliva on a toothbrush, from blood or hair or bones.
Step 2:
- The DNA is then digested with restriction enzymes. These enzymes cut the DNA at specific recognition sites. They will cut it into fragments, which will vary in size from individual to individual.
What are the 6 steps in DNA profiling?
Step 2: The DNA is then digested with restriction enzymes. These enzymes cut the DNA at specific recognition sites. They will cut it into fragments, which will vary in size from individual to individual.
Step 3:
- The fragments are separated by gel electrophoresis and stained. Larger fragments travel the shortest distance in the gel.
What are the 6 steps in DNA profiling?
Step 3: The fragments are separated by gel electrophoresis and stained. Larger fragments travel the shortest distance in the gel.
Step 4:
- A banding pattern can be seen.
What are the 6 steps in DNA profiling?
Step 4: A banding pattern can be seen.
Step 5:
- The DNA to which the individual’s is being compared to is treated with the same restriction enzymes and also subjected to electrophoresis.
What are the 6 steps in DNA profiling?
Step 5: The DNA to which the individual’s is being compared to is treated with the same restriction enzymes and also subjected to electrophoresis.
Step 6:
- The banding patterns of the DNA samples can then be compared.
The first method used involved restriction fragment length polymorphism analysis. This method is laborious and is no longer used. What is used now?
- Short tandem repeat (STR) sequences of DNA are used.
- These are highly variable short repeating lengths of DNA.
- The number of STRs varies from person to person.
What is separated by electrophoresis?
Short tandem repeat sequences.
What are two features of STRs?
- Each STR is polymorphic (has more than one form).
- The number of alleles in the gene pool for each one is small
Why are 13 STRs analysed simultaneously?
Although each STR is present in between 5% and 20% of individuals, the chances of the same two people sharing STR sequences at all the loci is 1x10^18.
Why must samples be treated carefully?
- This technique is very sensitive, and even a trace of DNA left when someone touches an object can produce a result.
- Samples must be treated carefully to prevent contamination.
Why is it useful that DNA can be stored for many years?
-If a crime case is unsolved, it can then later be used to assess new evidence.
- Why do half of the STR fragments come from the mother and half from the father?
- How can this be used to establish maternity/paternity?
- Because half of every child’s genetic information comes from the mother and half from the father.
- By comparing DNA profiles of the mother, father and child.
