DNA Profiling and Genetic Inheritance Notes

DNA Profiling Overview

  • DNA profiling involves comparing DNA fragments from a suspect with samples from a crime scene to establish a connection or inconsistency.
  • Key to this process is identifying DNA segments that match or do not match between the suspect's DNA and the crime scene DNA.

Comparing Suspects with Crime Scene DNA

  • Suspect One:
    • Has a significant DNA segment that is larger than any segment from the crime scene.
    • Inconsistency noted – no corresponding fragment found in crime scene data.
  • Suspect Two:
    • Identified spots match with crime scene DNA.
    • One spot consistent; can be stated as "consistent with the crime scene DNA".
  • Suspect Three:
    • No matches in the corresponding data spots – all inconsistent except for one spot where everyone shows a match.
    • This indicates some potential connections but overall many inconsistencies.

Key Terminology

  • Consistent: When a suspect’s DNA matches with the crime scene fragments indicating potential involvement.
  • Inconsistent: When the DNA does not match, indicating a lack of connection.

Assembling DNA Samples

  • DNA samples must be sufficient in size and quantity to yield results; scant samples (like a single blood drop) won’t be sufficient for analysis.
  • High molecular weight DNA is needed to show clear differences in profiling.
  • Barry Shek (Innocence Project co-founder) stressed needing adequate samples for successful DNA profiling.

Understanding Genetic Inheritance Through STR Data

  • Study of Short Tandem Repeats (STR) helps in identifying relationships based on shared alleles.
  • Parental Analysis:
    • Each individual receives genetic material from both parents; comparisons are made to verify potential familial relationships.
  • Example:
    • VWA Locus:
    • Tsar: 15, 16
    • Tsarina: 15, 16
    • Anna: 16 (possible to inherit from Tsar)
      • Anna: 14 (no inheritance possible from either parent)
    • Anna has alleles that can't be matched to either parent indicating her potential non-filiations.

Conclusion of Familial Connections

  • If a child presents alleles that cannot be accounted for by either parent, it indicates that the individual is not biologically related to those parents.
  • Anna's Case:
    • Multiple alleles present not matching with Tsar or Tsarina -> conclusion of non-biological connection.
  • Genetic markers and sex chromosomes:
    • Girls have XX, boys have XY attributes; must also verify throughout testing.

Mitochondrial DNA Analysis

  • Importantly, for maternal verification, mitochondrial DNA (mtDNA) must be consistent between mother and child.
  • If mtDNA doesn’t match, it suggests a lack of maternal connection, proving Anna isn’t the daughter of the Tsarina.

Summary Statement

  • For Anna, the final statement is crucial:
    • "Anna has alleles that are not from the Tsar or Tsarina; therefore she is not their child."