DNA profiling

Question 1

What is genetic fingerprinting?

Answer 1

A technique used by scientists, based on the fact that DNA of every individual (except identical twins) is unique, to identify and evaluate the genetic information.

Question 2

What is a process used in DNA profiling?

Answer 2

Gel electrophoresis

Question 3

What can Gel electrophoresis be used for ?

Answer 3

to separate large molecules on the basis of their size, electric charge, and other physical properties.

Question 4

What is step 1 of gel electrophoresis ?

Answer 4

DNA is often cut up into smaller pieces. Called a restriction digest, and it produces a range of DNA of different lengths.

Question 5

What is step 2 of gel electrophoresis?

Answer 5

DNA samples are placed in wells and covered with a buffer solution that gradually dissolves them into solution.

Question 6

What is step 3 of gel electrophoresis ?

Answer 6

By applying an electric field to the solution, the molecules move towards one or other electrode depending on the charge on the molecule itself. DNA is negatively charged because the phosphates have a negative charge.

Question 7

What is step 4 of gel electrophoresis ?

Answer 7

Molecules of different sizes (molecular weights) become separated (spread out) on the gel surface.

Question 8

What is step 5 of gel electrophoresis?

Answer 8

These can be visualized by applying dyes or radio-labelled probes

Question 9

What is step one of genetic fingerprinting ?

Answer 9

DNA is extracted from a sample (blood, hair, semen, skin).
if only a small amount of DNA is available it can be amplified using the polymerase chain reaction (PCR).

Question 10

What is an alternative to step 1 of genetic fingerprinting?

Answer 10

• Cells are broken down to release DNA.
• The DNA is cut into millions of small fragments using restriction endonucleases. - The sections of DNA that are cut out are called restriction fragments.

Question 11

What is step 2 of genetic fingerprinting ?

Answer 11

• Fragments are separated on the basis of size using a process called gel electrophoresis.
• DNA fragments are injected into wells and an electric current is applied along the gel.
• DNA is negatively charged so it is attracted to the positive end (anode) of the gel.

Question 12

What is step 3 of genetic fingerprinting ?

Answer 12

• DNA is separated into bands according to size of the fragments.
• The smaller the fragment – the faster it moves

Question 13

What is step 4 of genetic fingerprinting?

Answer 13

• The gel is immersed in alkali in order to separate the double strands into single strands.
• The pattern of fragments are transferred to a nylon membrane by a process called Southern blotting.

Question 14

What is step 5 of genetic finger printing ?

Answer 14

• Radioactive probes are used to attach to the core sequences (hybridisation).
• The probes have base sequences which are complementary to the core sequences.
• Any probes not bound are washed off.
  The membrane is dried.

Question 15

What is step 6 of genetic fingerprinting ?

Answer 15

• The nylon sheet is placed under X-ray film.
• The radioactive probes on the DNA fragments expose the film.
• This produces visible patterns of light and dark bands which are unique to each individual.
• The pattern of fragment distribution is then analysed.
• The pattern of the bands is unique to every individual (except identical twins).