CSI Analysis Instructions

Classroom Procedures

  • Teacher checks for phones:

    • Highly emphasized focus on removing personal distractions during class. Names called out: Trinity, Daniela, Brandon, Ethan.

  • Reminder about binders:

    • Students reminded that binders should not leave the classroom.

    • Incorrect binder retrieved; confusion addressed.

  • Importance of completing pre-lab questions:

    • Students warned they will lose points without teacher’s signature.

Lab Results Discussion

  • Display of gel results:

    • Gels laid out on a light box for visibility.

    • General positivity about the results from most tables.

    • Issues noted with:

      • Table 5 (results visibility)

      • Table 6 (color discrepancy).

  • Explanation of gel binding properties:

    • DNA appears darker against the gel background.

    • Importance of examining gels directly for accurate results.

Analyzing the Gel

  • Initial instructions for gel processing:

    • Students instructed to label and draw lines indicating where bands are present.

    • Recommended using a pencil that can be distinguished on the gel’s gray surface.

  • Questions guiding students in reflection:

    • Identification of contents in each well:

      • First well contains a ladder (reference for size).

      • Second to fifth wells contain crime scene samples labeled (A, B, C, D).

  • Clarification on PCR process:

    • Focus on amplifying the number of repeats of a sequence of DNA bases.

    • Ladder indicates the number of repeats from top (15) to bottom (1).

  • Clarification on genetic inheritance:

    • Importance of knowing that individuals inherit two copies of each gene (one from each parent).

Genotype Analysis

  • Discussion of genotype from samples:

    • Students need to count repeats from gel results to determine their samples' genotypes.

    • Example given: gene analysis of seven repeats indicated on the gel.

  • Instructions on recording observations:

    • Students must ensure their observations match their personal gel output, not the examples shown by the teacher.

Question Guidelines

  • Overview of key questions for the students:

    • Did all samples generate PCR products?

      • Justification needed if not; students should analyze possible reasons for failure, such as issues in the PCR setup or sample degradation.

    • What is the genotype of each sample?

      • How to find this in the results table by counting the number of bands and referring to which bands correspond to specific repeats.

    • Does the crime scene DNA sample have a matching genotype with any suspect?

      • Specify which suspect (A, B, C, D) the crime scene sample matches with; students should give clear comparisons based on band patterns and observed repeats.

    • Interpretation of results regarding investigation inclusions/exclusions:

      • Requires justification; students should explain the implications of their findings, whether it supports or excludes potential suspects based on genetic match or mismatch, detailing the relevance to the case.

    • Discussion on testing against multiple suspects:

      • How many suspects were tested, and implications of finding a match in a larger pool of suspects; students should discuss the significance of a match in terms of probability and how it might affect the investigation's direction.

  • Emphasis on thorough explanations in answers:

    • Encourage students to clearly articulate their reasoning, use evidence from the gel results, and understand the significance of genotyping in forensic investigations.

Final Instructions

  • Completion tasks:

    • Fill in the data table, mark the gel appropriately, and glue it down.

  • Questions about the tape label clarified; not needed once glued down.

  • Students encouraged to approach the teacher with any remaining questions.