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DNA TESTING
Class Notes
DNA
 DNA stands for Deoxyribonucleic Acid.
 It is a molecule in your body that carries your
genetic information.
Chromosomes
 Chromosomes are tightly compacted DNA.
 Human beings have a total of 23 pairs of
chromosomes.
Genes
 Genes are your actual genetic material located
on your chromosomes / DNA.
Chromosomes
 The first 22 pair of chromosomes are called
Autosomes.
 The 23rd chromosome is known as the sex
chromosome because it determines the gender
of the individual.
Gametes
 Sex cells are known as gametes.
 The female gamete is called the egg cell or ova.
 The male gamete is called spermazoa or sperm.
 The male sperm carry either the x or y
chromosome into the egg cell, so therefore
determine the sex of the cell.
Alleles
 Alleles are a specific form of a gene.
 An example would be an allele for eye color is
blue eyes or brown eyes.
 The genotype is the genetic makeup of a gene.
The phenotype is the physical characteristic of a
gene.
Homozygous vs.
Heterozygous Alleles
 Homozygous Alleles have identical genotypes.
 Heterozygous Alleles have different genotypes.
Example of Homozygous Brown Eyes: BB
Example of Heterozygous Brown Eyes: Bb
Paternity Tests
 To perform a paternity test, the blood group
genotypes of the suspected parents and
offspring are compared.
 Routine paternity tests also involve a test looking
for a specific antigen (HLA: Human Leukocyte
Antigen) on white blood cells.
 DNA testing is also done to establish paternity
beyond 99%
Testing for Semen
 Serologists look for the enzyme, acid phosphate.
The color test for this enzyme is called the acid
phophatase test.
 If acid phosphate is present they know it is most
likely semen.
Testing for Semen
 Semen can also be identified through
microscopic examination.
 The normal male releases 250 – 600 million
spermatozoa during ejaculation.
Spermatozoa are not often
found in seminal fluid due
to:
 1) they bind tightly to cloth such as underwear.
 2) they are extremely brittle when dry and easily
disintegrate.
 3) some crimes involve individuals with little to no
sperm count. This is called Oligospermia or
Aspermia.
Conclusive Spermazoa Test
 The test most often used to absolutely prove the
presence of semen is a test looking for the
protein called prostate specific antigen or p30.
The following will be
collected from a rape
victim:
 1) Pubic combings.
 2) Pubic hair as a standard / reference sample.
 3) External genital / dry-skin areas.
 4) Vaginal swabs / smear.
 5) Cervix Swab
 6) Rectal Swab and Smear
The following will be
collected from a rape
victim:
 7) Oral Swabs and Smear
 8) Head Hairs
 9) Blood Sample
 10) Fingernail Scrapings
 11) All Clothing
 12) Urine Specimen
Male suspects
 1) All Clothing
 2) Pubic Hair Combings
 3) Pulled head and pubic hair as a standard /
reference sample
 4) Penile swabs within 24 hours of assault
 5) Blood Sample or Buccal Swab for DNA