Bloodstain Pattern Analysis Quiz

Bloodstain Pattern Analysis

• Bloodstain pattern analysis (BPA) is a controversial and subjective practice that studies bloodstains at a crime scene to draw inferences about the crime's nature, timing, and details.
• BPA is used primarily for homicide and violent crimes where blood is present, and is claimed to aid in crime scene reconstruction.

History of Bloodstain Pattern Analysis

• Bloodstain pattern analysis has been used informally for centuries, but the first modern study of bloodstains was in 1895 by Dr. Eduard Piotrowski.
• LeMoyne Snyder's book "Homicide Investigation" (1941) briefly mentioned bloodstains, but it didn't lead to a systematic analysis.
• In 1952, a "Dragnet" radio episode referenced bloodstain pattern analysis to reconstruct a shooting incident.

Acceptance as Valid Evidence

• Between 1880 and 1957, courts in Michigan, Mississippi, Ohio, and California rejected expert testimony for bloodspatter analysis.
• In 1957, the California Supreme Court became the first American court to accept expert testimony examining bloodstains.
• Herbert Leon MacDonell's research and book "Flight Characteristics and Stain Patterns of Human Blood" (1971) led to the widespread use of BPA in American courts.
• The International Association of Bloodstain Pattern Analysts was founded in 1983.

Controversy and Criticisms

• The 2009 National Academy of Sciences report harshly criticized BPA and the credentials of its analysts.
• Judges have largely ignored the report's findings and continue to accept BPA as expert evidence.
• In 2021, a study published showed that BPA conclusions were often erroneous and contradicted other analysts.

Physics of Blood

• Blood is composed of erythrocytes, leukocytes, and thrombocytes suspended in plasma.
• When a blood vessel is damaged, blood moves outside the circulatory system, following the laws of physics.
• Gravity, internal pressure, and external forces can affect blood's behavior.
• Blood is a shear-thinning, non-Newtonian fluid with three main physical properties: viscosity, surface tension, and density.

Bloodstain Types

• Bloodstains can present differently depending on the situation and material they appear on.
• Impact spatter is the most common bloodstain pattern type, occurring when an object hits a source of blood.
• Bloodstains may be hard to examine on porous surfaces, and may be distorted.### Bloodstain Pattern Analysis
• Bloodstain pattern analysts consider the angle of impact to determine the origin and the amount of force behind it.
• Variations in external forces can cause satellite drops.
• Point of origin can be determined by finding the "area of convergence" for the blood droplets.
• The stringing method involves drawing lines from each blood splatter and finding the area in which all the blood intersect.

Impact Spatter

• Impact spatter is the most common bloodstain pattern type in a crime scene.
• It occurs when an object hits a source of blood.
• In impact blood spatter patterns, blood is often circular and not elongated.

The Physics of Blood

• Blood is composed of three components suspended in plasma: erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).
• Blood behaves as a shear-thinning, non-Newtonian fluid due to its viscosity, surface tension, and density.

Bloodstain Types

• Bloodstains can present themselves differently depending on the situation and the material on which they appear.
• Bloodstains may be hard to examine on porous surfaces such as fabric, and may be distorted.
• Angle of impact can be determined by measuring the length and width of the blood droplet and using the formula sin(A) = width/length.

History of Bloodstain Pattern Analysis

• The discipline of bloodstain pattern analysis was not widely accepted until it was promoted by Herbert Leon MacDonell.
• MacDonell researched bloodstains with a grant from the United States Department of Justice and published his research in the book "Flight Characteristics and Stain Patterns of Human Blood" (1971).
• The first formal bloodstain training course was given by MacDonell in 1973 in Jackson, Mississippi.

Criticisms and Controversies

• In 2009, the National Academy of Sciences published an examination of forensic methods used in United States courts, which harshly criticized bloodstain pattern analysis.
• The report questioned the reliability and admissibility of bloodstain pattern analysis as evidence in court.
• Research has suggested that many of the central hypotheses of bloodstain analysis remain untested, and that existing analysts often made incorrect assumptions or other errors in their analyses.

Mendelian Inheritance

• Mendelian inheritance is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866.
• The principles of Mendelian inheritance were named for and first derived by Gregor Johann Mendel, a nineteenth-century Moravian monk.

Key Principles of Mendelian Inheritance

• Characters are unitary, that is, they are discrete (e.g. purple vs. white, tall vs. dwarf).
• Genetic characteristics have alternate forms, each inherited from one of two parents.
• One allele is dominant over the other.
• Gametes are created by random segregation.
• Different traits have independent assortment.

Polygenic Traits

• Traits controlled by two or more genes are said to be polygenic traits.
• Polygenic traits often show a wide range of phenotypes.

Non-Mendelian Inheritance

• Non-random segregation of chromosomes is a deviation from the usual distribution of chromosomes during meiosis and in some cases of mitosis.
• Gene conversion can be one of the major forms of non-Mendelian inheritance.
• Infectious heredity is another form of non-Mendelian inheritance.
• Genomic imprinting represents yet another deviation from Mendelian inheritance.### Mendelian Inheritance
• Mendel discovered heredity units, called "factors" (now known as genes) that account for variations in inherited characteristics.
• Each gene has alternative forms, called alleles, that can be dominant or recessive.
• An organism inherits two alleles for each gene, one from each parent, which can be homozygous (same alleles) or heterozygous (different alleles).

Genotype and Phenotype

• The genotype of an individual is the combination of all its alleles.
• The phenotype is the result of the expression of all genetically determined characteristics and the environment.

Law of Dominance and Uniformity

• In a heterozygote, the dominant allele will mask the recessive allele, and the recessive trait will only be expressed if the individual is homozygous for the recessive allele.
• The F1 offspring of a cross between two homozygous parents will always show the dominant trait.

Non-Mendelian Inheritance

• Non-Mendelian inheritance occurs when traits do not segregate according to Mendel's laws.
• Types of non-Mendelian inheritance include:
  • Incomplete dominance
  • Co-dominance
  • Multiple alleles
  • Polygenic traits
  • Genetic linkage
  • Epistasis
  • Sex-linked inheritance
  • Extranuclear inheritance

Incomplete Dominance

• Incomplete dominance occurs when the dominant allele does not completely mask the recessive allele.
• The F1 offspring will have an intermediate phenotype, and the F2 offspring will segregate in a 1:2:1 ratio.

Co-dominance

• Co-dominance occurs when both alleles of a gene are expressed in the phenotype.
• Examples include the ABO blood type and the colour of certain chicken breeds.

Multiple Alleles

• Multiple alleles occur when a gene has more than two alleles.
• Examples include the genes for rabbit coat colour and human ABO blood type.

Epistasis

• Epistasis occurs when the expression of one gene is affected by the presence of another gene.
• Examples include the genes for dog coat colour and the Extension-locus.

Sex-linked Inheritance

• Sex-linked inheritance occurs when a gene is located on the X or Y chromosome.
• Examples include colour blindness and haemophilia.

Extranuclear Inheritance

• Extranuclear inheritance occurs when genetic traits are inherited through the cytoplasm of the ovule.
• Examples include the transmission of chloroplast and mitochondrial DNA.

Pedigree

• A pedigree is a diagram that shows the occurrence and appearance of phenotypes of a particular gene or organism and its ancestors.
• Pedigrees use standardized symbols to represent individuals and relationships.
• Analysis of a pedigree can determine whether a trait has a dominant or recessive pattern of inheritance.

Test your knowledge of Bloodstain Pattern Analysis (BPA) with this quiz! Explore the key concepts, techniques, and controversies surrounding this forensic practice used to analyze bloodstains at crime scenes. Assess your understanding of BPA's role in crime scene reconstruction and its potential impact on criminal investigations.