Problem 3 - Campbell Biology Concepts & Connections

Question

The DNA profiles used as evidence in a murder trial look something like supermarket bar codes. The pattern of bars in a DNA profile shows a. the order of bases in a particular gene. b. the presence of various-sized fragments of DNA. c. the presence of dominant or recessive alleles for particular traits. d. the order of genes along particular chromosomes.

Step-by-Step Solution

Answer

b. the presence of various-sized fragments of DNA.

Step 1: Identify the Nature of DNA Profiles

Understand that DNA profiles are visual representations created during DNA analysis. They resemble barcodes and are not a direct sequence of DNA bases or genes.

Step 2: Examine Option A

Option A states 'the order of bases in a particular gene.' DNA profiles do not show the exact sequence of bases; instead, sequencing methods do this. Therefore, Option A is incorrect.

Step 3: Examine Option B

Option B states 'the presence of various-sized fragments of DNA.’ This accurately describes the output of techniques like gel electrophoresis used in DNA profiling, where fragments are separated by size and visualized as bands. Thus, Option B is correct.

Step 4: Examine Option C

Option C states 'the presence of dominant or recessive alleles for particular traits.’ This is a genetic interpretation that requires further genetic analysis, not just a DNA profile. Option C is incorrect.

Step 5: Examine Option D

Option D states 'the order of genes along particular chromosomes.’ DNA profiles do not show gene order; they show fragment sizes resulting from restriction enzyme cuts. Hence, Option D is incorrect.

Step 6: Choose the Correct Answer

Based on the detailed analysis, Option B 'the presence of various-sized fragments of DNA' is the correct description of what DNA profiles in a murder trial show.

Key Concepts

DNA analysis

DNA analysis involves examining an individual's genetic material to identify unique patterns. This can be important in various fields like criminal investigations, paternity tests, and ancestry tracing. During DNA analysis, scientists look at specific regions of the DNA that vary greatly among individuals. These variations can help pinpoint identity with high accuracy. The result is a DNA profile, which looks like a series of bars or lines, similar to a supermarket barcode. This visual representation highlights differences in DNA between individuals. In criminal cases, matching DNA profiles can link suspects to crime scenes or identify victims.

gel electrophoresis

Gel electrophoresis is a lab technique used to separate DNA fragments by size. Here’s how it works: First, scientists cut DNA with special enzymes called restriction enzymes. These cuts create fragments of various lengths. The DNA fragments are then placed in a gel matrix, and an electric current is applied. Because DNA is negatively charged, it moves towards the positive end of the gel. Smaller fragments move faster and travel further through the gel than larger ones. After the electrophoresis is completed, the DNA fragments form distinct bands that can be visualized using a dye. This pattern of bands is what we see in a DNA profile used in forensic analysis.

DNA fragments

In DNA analysis, DNA fragments are pieces of DNA that have been cut by restriction enzymes at specific sequences. These fragments vary in length depending on the individual's unique genetic code. When placed in a gel electrophoresis setup, the movement of these fragments creates a pattern. The presence of various-sized DNA fragments is crucial for generating a distinguishable DNA profile. Each individual has a unique pattern of DNA fragments, which makes DNA profiling a powerful tool for identification. To visualize and understand these fragments, a gel electrophoresis technique is used. This process results in distinct bands for each fragment, which together create a DNA profile.