Problem 6 - Biology: Science for Life with Physiology

Question

Which of the following is not part of the procedure used to make a DNA fingerprint? A. DNA is amplified by PCR; B. DNA is placed in a gel and subjected to an electric current; \(\mathbf{C}\). The genes that encode fingerprint patterns are cloned into bacteria; D. DNA from blood, semen, vaginal fluids, or hair root cells can be used for analysis.

Step-by-Step Solution

Answer

Option C is not part of DNA fingerprinting.

Step 1: Review Each Option

We need to examine what each option entails in the context of DNA fingerprinting. Option A - PCR is used to amplify DNA, which is part of DNA fingerprinting. Option B - DNA is subjected to gel electrophoresis, also central to DNA fingerprinting. Option D - DNA from various sources is analyzed, which is part of the process.

Step 2: Evaluate the Irrelevant Option

Option C mentions cloning the genes that encode fingerprint patterns into bacteria. This does not align with standard DNA fingerprinting procedures. Fingerprint analysis focuses on identifying DNA patterns, not cloning.

Key Concepts

PCR

Polymerase Chain Reaction (PCR) is a powerful technique used in DNA analysis and DNA fingerprinting to amplify small quantities of DNA. This means it makes millions of copies of a specific DNA segment, enabling scientists to work with sufficient material for analysis.
PCR is essential when the DNA sample is limited or degraded, such as a small drop of blood or a single hair follicle. The process involves several key steps, executed in a machine called a thermocycler:

• Denaturation: Heating the DNA to separate the two strands.
• Annealing: Cooling so primers can bind to each DNA strand.
• Extension: DNA polymerase enzyme adds nucleotides to form new strands.

Through these cycles, PCR exponentially increases the amount of DNA. This prepared, amplified DNA can then be used in subsequent processes, like gel electrophoresis, making PCR a fundamental initial step in DNA fingerprinting.

gel electrophoresis

Gel electrophoresis is a critical method used to separate DNA fragments based on their size, which is crucial for DNA fingerprinting. Once DNA is amplified using PCR, it is loaded onto a gel, and an electric current is applied.
The DNA fragments move through the gel towards the positive end because DNA is negatively charged. Smaller fragments move faster and farther than larger ones, leading to their separation.
To visualize the results, the gel is often stained with a dye that binds to DNA. When placed under UV light, the DNA fragments appear as distinct bands. The resulting pattern is unique to each individual, akin to a fingerprint. This capability makes gel electrophoresis an indispensable tool in DNA analysis and criminal investigations.

DNA analysis

DNA analysis involves examining the unique patterns in an individual's DNA to gather information for research, medical diagnostics, or forensic investigations. In DNA fingerprinting, the process starts with the collection of a sample that contains cells with DNA, like blood, saliva, or hair.
Following collection, the DNA is isolated, amplified through PCR, and separated by gel electrophoresis. The final step in DNA analysis is to compare these DNA band patterns across different samples.

• Identifying matching patterns can help to confirm a person's identity.
• Comparing DNA from a crime scene to a suspect's DNA can help in criminal investigations.
• DNA samples from different individuals can be compared to establish family relationships.

The combination of PCR and gel electrophoresis in achieving clear, precise comparisons makes DNA analysis an invaluable technique in various fields of study and application.