From what species did the blood originate? Blood & Heredity If blood is suspected, a criminalist must answer the following questions: Is it blood? From what species did the blood originate? If the blood is human, how closely can it be associated with a specific person?

Kastle-Meyer color test Preliminary color test, tests for the presence of hemoglobin in blood (peroxidase) When a bloodstain, K-M reagent, and hydrogen peroxide are mixed, it produces a deep pink color Its not specific for blood, potato and horseradish will turn the reagent pink, but a positive K-M test is still highly indicative of blood The Kastle-Meyer blood test is sensitive to dilutions of one part blood to ten thousand parts water

Hemastix strips Urine dipstick is useful as a presumptive field test for blood (peroxidase activity in hemoglobin) Strip can be moistened with distilled water and placed in contact with a bloodstain The appearance of a green color change indicates the presence of blood Positive reaction will take place in less than 30 seconds Screens for minute amounts of blood and will respond to trace levels of hemoglobin Detecting blood at such dilute concentrations is approximately equivalent to detecting 5-20 intact red blood cells per microliter of fluid.

Luminol The reaction of luminol with blood produces light After spraying luminol, darken the room, any blood will produce a faint blue glow called luminescence It is extremely sensitive May reveal blood traces or patterns that could have gone unnoticed in lit areas It does not interfere with DNA testing

Precipitin Test Once characterized as blood, need to determine whether its human or animal The standard test is the precipitin test Animals are injected with human blood, antibodies form that react with the invading human blood antigens Investigator recovers antibodies by bleeding the animal and isolating the serum This serum has antibodies that reacted with the human antigens (human antiserum) Same thing can be done with any animal to produce dog antiserum, cat antiserum, etc.

Performing precipitin tests on blood Place an amount of human antiserum that was made in the rabbit in a test tube Layer bloodstain on top of that If it is truly human blood, the human blood will react with the antibodies in the antiserum and form a cloudy band between the two liquids

Gel Diffusion Antibodies and antigens diffuse or move toward one another on a plate coated with a gel The bloodstain and human antiserum are placed in holes opposite each other on the gel If the blood is human, a line of precipitation forms where the antigens and antibodies meet Once it is determined that it is of human origin, DNA tests are performed

Blood can also be examined microscopically Bird Blood Cat Blood Dog Blood Fish Blood Frog Blood Snake Blood Blood can also be examined microscopically Human Blood Horse Blood

Heredity All antigens are genetically determined traits Inherited from parents and are part of the biological makeup once that person has been conceived Genetic material is transferred by genes Genes are located on chromosomes that are located inside the nucleus Almost all human cells have 46 chromosomes The only exceptions are the gametes, which are sperm and egg cells, which contain 23 chromosomes

Sex Cells Females carry X chromosomes Males carry X and Y chromosomes When an X sperm fertilizes the female egg, it now contains XX, which is female When a Y sperm fertilizes the female egg, it now contains XY, which is male The sperm cell determines the chromosome pair, so males determine the sex of the child

There are three alleles (A,B,O) BLOOD GENETICS There are three alleles (A,B,O) The first two are A and B and are co-dominant and produce antigens on the surface of red blood cells The third allele is O and is recessive AA for type A It can exist in heterozygous situations in type A as AO or in type B as BO but is not expressed Homozygous BB for type B When the gene is homozygous OO it is said to be type O AB for type AB

Genotype and Phenotype A pair of genes makes up the genotype No known lab test can determine an individual’s A-B-O genotype A phenotype is a person’s outward characteristic, such as having A blood This still does not tell whether the genotype is AA or AO It can only be determined by studying the family history

Paternity testing No blood can appear in a child unless it is present in at least one of the parents Has important implications in disputed paternity cases, which are encountered in civil, not criminal, cases Many cases can be solved by comparing the blood types of mother and suspected father If the father can not be excluded, then all that can be said is that he may be the father because of blood typing, but does not strictly mean he is the father Further testing, such as DNA, will be required