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.