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Piecing Together an Identity
Blood Group Antigens
• Antigens are defined as substances recognized
by the body, causing the body to produce an
antibody to react specifically with it.
• Antibodies are proteins that react specifically
with an antigen
• When a blood antigen and antibody react with
each other agglutination occurs
Blood Typing vs Secretor Status
If the saliva of a secretor is mixed with the
antiserum or lectin specific for its blood
group substance then most of the antibody in
the antiserum will bind to the blood group
substance in the saliva. So when you add the
red blood cells for that type no clumping or
very little clumping should be observed. This
is the opposite of what you would see during
a traditional blood test.
Importance of Gender
• Establishing individual identity is an
imperative aspect of any investigative
procedure. Determination of gender helps in
investigations by narrowing down potential
pools of victims of potential pools of
suspects.
XXChromosome
Inactivation
Chromosome Inactivation
• Since cells in a male contain a single X
chromosome and cells in a female contain two X
chromosomes, females contain twice as many
copies of the genes on the X chromosome per
cell as do males. To equalize the dosage of X
chromosome genes between the two sexes, one
of the two X chromosomes in each cell of all
female mammals is inactivated early in
embryonic development by becoming very
tightly wound up or condensed. These
condensed chromosomes are Barr Bodies.
Barr Bodies
Barr bodies allow one to
distinguish between male
and female mammals but
will not be able to tell if the
cell containing the Barr
body is human.
Secretor Status
• The term “secretor” refers
to the presence of A, B,
and H substances in the
body fluids, such as in
sweat, tears, saliva, and
serum.
• Secretor status is used
when blood or blood
products are too
degraded or not available.
Amelogenin
• The amelogenin gene for tooth pulp is six
bases shorter on the X chromosome than on
the Y chromosome. When amplified and
examined on an agarose gel, a female will
have one band, (two X’s) and a male will have
two bands one for the X and one for the Y.
• So the use of this gene is a common identifier
to determine gender.
Mitochondrial DNA
• With nuclear DNA, a child receives half of its
DNA from each parent in any give strand, half
of the sequence will match the mother’s DNA
and the other half will match the father’s
DNA.
• In the case of mitochondrial DNA, an exact
copy is inherited from your mother as it has
been passed from all of the female relatives
on your mother’s side of the family.
Heteroplasmy
• A very small portion of the mitochondrial DNA
might be a contribution from the male parent.
• This occurs only if the tail of the sperm enters
the egg during the process of fertilization.
• The head of the sperm is an empty vessel that
contains the DNA of the male parent.
• The tail of the sperm must contain
mitochondria to supply energy for the process
of locomotion.