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DNA
(Ch 7)
DeoxyriboNucleic Acid
“The Blueprint of Life”
DNA Structure

nuclear DNA
is found in
the nucleus
of cells in
chromosomes
# of Chromosomes


in human somatic cells, 46
chromosomes (23 pairs with one from
mom, one from dad)
in human sex cells, only 23
chromosomes
DNA Structure

mitochondrial
DNA is a
circular loop
and ONLY
inherited
from mother
DNA Structure

composed of smaller units
called nucleotides
- phosphoric acid
(phosphate)
- deoxyribose sugar
- nitrogenous base
(Adenine, Thymine,
Guanine or Cytosine)
DNA Structure



shape:
double helix
(twisted ladder)
side/rails:
sugar-phosphate
backbone
steps/rungs:
N bases
Watson & Crick’s double
helix
Nitrogenous Bases


PURINES (big) and PYRIMIDINES (small)
A&G
C&T
purines hydrogen bond with pyrimidines
A=T
C=G
triple bond
double bond
Adenine
bonds only
to Thymine
Cytosine
bonds only
to Guanine

Be able to find the complementary
DNA strand given a DNA sequence:
5’ CCGATTACGGAA 3’
3’ ?

ANS: GGCTAATGCCTT 5’


Genes and Alleles



alleles are alternative forms of a gene;
one allele from mom, one from dad
human genome includes the total
amount of DNA in a cell
only ~1.5% of the DNA is coding
(makes proteins) – the rest is “junk
DNA”
Function of DNA

Hereditary instructions

Chemical code for every trait
“Blueprint” for
making proteins

Chromosome DNA Code
Genes are segments
of DNA that code
for a single trait
The code is in sets of
3 (triplicate) called
CODONS
Every codon = 1
amino acid in the
protien
Acid
Acid
Sugar-T-A-Sugar
Acid
Acid
Sugar-G-C-Sugar
Acid
Acid
Sugar-C-G-Sugar
Hair
Color
Eye
Color




DNA code:
Ccc gga tta ggc
How many amino
acids will this
encode for?
=4
DNA Replication
during mitosis –
when the
chromosomes
double during late
interphase
2N
2N
DNA Replication
1. DNA unwinds
2. DNA unzips using DNA polymerase
3. Corresponding base pairs
line up
4. DNA reforms
5. Zips back up and winds back up
DNA Identification




differences in DNA sequences
(lengths, sequences of bases):
polymorphism
use VTNR and STR in noncoding
section to identify individuals
Compare 13 regions to build a bank
Human differ <0.1% from each other

According to the Innocence project,
about 200 people who have been
jailed have been proven innocent and
released from prison using DNA
evidence
DNA Identification


Tissue Matching
- 2 samples with same pattern are
same person (crime scene vs. suspect)
Inheritance Matching
- bands on a child must be present in
one of the parents
DNA Typing


portions of the DNA molecule contain
sequences of bases that are repeated
numerous times are known as VNTR
to a forensic scientist, these tandem
repeats offer a means of distinguishing one
individual from another through DNA typing
Restriction Enzymes

can be thought of as highly specialized
scissor that cuts a DNA molecule when
it recognizes a specific sequence of
bases.
PCR Testing

with the knowledge
of how DNA
replicates, forensic
scientist are able to
use PCR to take
minute quantities
of DNA and
multiply it many
millions of times to
make a larger
sample
Electrophoresis


materials are
forced to move
across a gelcoated plate
under the
influence of an
electrical current
substances such
as DNA can be
separated and
characterized
 bands and widths are significant in matching
samples of DNA
 DNA fingerprinting can
(a) match crime scene DNA with a suspect,
(b) determine maternity, paternity, or match to
another relative,
(c) eliminate a suspect,
(d) free a falsely imprisoned individual, and
(e) identify human remains.
CODIS


perhaps the most significant tool to arise
from DNA typing is the ability to compare
DNA types recovered from crime scene
evidence to those of convicted criminals
CODIS (COmbined Dna Index System) is a
computer software program developed by
the FBI that maintains local, state, and
national databases of DNA profiles from
convicted offenders, unsolved crime scene
evidence, and of missing persons
DNA Sources


saliva, blood, seminal fluid, skin, hair
INDIVIDUAL EVIDENCE
Pedigrees
Dominant trait- a trait seen in every generation
Distributed equally between males and females
Recessive trait – seen rarely in a family
Sex-linked trait- seen more in males than females.
At least three fold more males than females
-Males inherit the gene from MOM
-Girls inherit the gene from DAD
-- gene found on the X chromosome
-So girls have two alleles for the gene
-Boys have one allele (NO CARRIERS)
-*** Must be able to do pedigrees and calculate
-Percent of genotype and phenotype possibilities