The Blackett Family DNA Activity
Introduction
Welcome to the Blackett Family DNA Activity. Bob Blackett is a DNA analyst. As part of his
training, he made a DNA profile of his own family using a technique called RFLP analysis. Family
studies are a good way to learn about DNA profiling and RFLP analysis because you can follow
the inheritance of DNA markers (alleles) from one generation to the next.
In this activity, you will:
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learn the concepts and techniques behind DNA profiling
interpret DNA autoradiograms
evaluate DNA profiles to determine familial relationships
There is also a sequel to this activity, Blackett Family DNA Activity 2 , where you will learn
about the most current method of DNA profiling based on analysis of short tandem repeat
polymorphisms.
RFLP Analysis
Anatomy of An Autorad
Questions on Activity
Career of a DNA analyst
back row: grandparents Norma and Fred
middle row: parents Robert and Anne
front row: children David and Katie
Blackett Family DNA Activity
Restriction Fragment Length Polymorphism analysis
In RFLP analysis,
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RF stands for Restriction Fragments. Those are the fragments of DNA that were cut by
restriction enzymes.
L stands for Length, and refers to the length of the restriction fragments.
P stands for Polymorphism, a Greek term that literally means "many shapes".
The lengths of some of the restriction fragments differ greatly between individuals, thus there
are many shapes, or lengths, of DNA possible.
Molecular biologists have identified regions of the human genome where restriction fragment
lengths are highly variable between individuals. These regions are called RFLP markers.
Blackett Family DNA Activity
Inheritance of RFLP markers
Humans have a total of 23 pairs of chromosomes. Each pair contains one chromosome from
mom and one from dad. The RFLP markers most commonly used for DNA profile analysis are
found on chromosomes 1, 2, 4, 5, 10 and 17. These RFLP markers are named after their
locations on these chromosomes. For example, the marker on chromosome 2 is called D2S44
(section 44 of chromosome 2). These chromosomal locations are also referred to as DNA loci
(from Latin: locus is singular, loci are plural). The DNA loci used in profile analysis are shown on
the karyotype below.
Blackett Family DNA Activity
Anatomy of the Autorad
Autorads are x-ray films
with dark bands
representing RFLP
markers. The bands are
found in lanes, and each
lane in this autorad
contains DNA fragments
from a different source.
In the autorad to the
left, the tops of the 15
lanes are numbered in
red.
Bands containing longer
fragments of DNA are
toward the top of the
autorad and bands
containing shorter
fragments are toward
the bottom.
This is where the
"Length Polymorphism"
of RFLP is important;
Because different
individuals will have
many different lengths
of DNA possible at the
location of an RFLP
marker, different people
will have bands at
different places.
Blackett Family DNA Activity
Anatomy of the Autorad
In lanes 13 and 14, the
DNA analyst loaded in
DNA from the
grandparents. Notice that
Norma and Fred do not
share any bands.
Although they are
married, they are not
"blood relatives" and you
would generally not
expect unrelated
individuals to have the
same bands.
Blackett Family DNA Activity
Anatomy of the Autorad
In lanes 8 and 9, the DNA analyst
loaded DNA fragments from
himself (Bob) and his wife (Anne).
Notice that Bob and Anne each
have 2 bands in their respective
lanes. At any given DNA locus,
most people have two bands.
Sometimes they only have one
band and sometimes they actually
have three.
Also notice that like Fred and
Norma, Bob and Anne do not
share any bands at this DNA locus.
Although Bob's top band is close
to Anne's bottom band, they are
not close enough to consider
them a match.
Blackett Family DNA Activity
Anatomy of the Autorad
As mentioned earlier, children
inherit 23 chromosomes from
their mother and 23 from their
father. In this autorad, we are
looking at the RFLP marker D1S7
located on chromosome 1.
In lanes 10 and 12, the DNA
analyst loaded DNA from his
children David and Katie. Each
child inherited one copy of the
D1S7 marker from their mother
and one copy from their father.
These markers show up as bands
on the autorad. Most people have
two bands because they inherit
one band from each of their
parents.
Note that David inherited his
mother's top band and his father's
top band. David's sister Katie,
however, inherited mom's bottom
band and dad's bottom band.
Sometimes siblings will inherit the
same bands from their parents,
although this is not the case for
David and Katie at this DNA locus
(i.e., they share no bands at D1S7).
Blackett Family DNA Activity
Anatomy of the Autorad
In lanes 4, 5, and 6 the DNA
analyst loaded DNA from 3
unrelated individuals. Notice how
none of their bands match with
one another. Unrelated individuals
will, however, occasionally share
bands. For example, in this case, it
appears that the top band in lane
4 could match the bottom band in
lane 9 (Bob's DNA).
DNA analysts are careful to always
use a control when performing
DNA analysis. In lane 3, Bob
loaded a DNA sample that should
always have bands in the same
place on an autorad. If the control
bands do not appear where the
analyst expects them to be, the
integrity of the rest of the
information in the autorad is often
questioned. If the control bands
do appear where they should be,
then the analyst has confirmation
that the autorad contains usable
information. In this case, the
control bands were good.
Blackett Family DNA Activity
Anatomy of the Autorad
Every autorad also has several
lanes containing DNA ladders.
Each band in these lanes contains
a known length of DNA. The
ladders are used to determine the
length of the DNA in bands in
other lanes.
Blackett Family DNA Activity
Evaluating the DNA profiles
D1S7
D2S44
D4S139
D10S28
Here are some questions to further your understanding of the Blackett Family Activity.
1. Are the grandparents maternal or paternal?
2. The autorad contains 8 alleles for the siblings tested. Which of the alleles and how many are
shared between each of the siblings?
3. Are any of the unknowns related to the family? If so, which ones?
4. Are any of the other unknowns tested related to each other? If so, which ones?
5. Are there any 1-locus matches between non Blackett family members?
Blackett Family DNA Activity 2
Overview
In this activity, you will learn the concepts and techniques behind DNA profiling of the 13 core
CODIS (Combined DNA Index System) "Short Tandem Repeat" loci used for the national DNA
databank. You will then have the opportunity to collect and interpret actual STR (Short Tandem
Repeat)data, and to answer one or more of the following questions:
1. How is STR data used in a DNA Paternity Test?
2. How can STR data from close relatives be used to create a genetic profile of a missing
person?
3. How much genetic diversity exists among siblings?
4. How does one calculate the probability for a specific DNA profile?
The Science of STR DNA Profile Analysis
STR Polymorphisms
Most of our DNA is identical to DNA of others. However, there are inherited regions of our DNA
that can vary from person to person. Variations in DNA sequence between individuals are
termed "polymorphisms" (many different forms, in this case, length). As we will discover in this
activity, sequences with the highest degree of polymorphism are very useful for DNA analysis in
forensics cases and paternity testing. This activity is based on analyzing the inheritance of a
class of DNA polymorphisms known as "Short Tandem Repeats", or simply STRs.
STRs are short sequences of DNA, normally of length 2-5 base pairs, that are repeated
numerous times in a head-tail manner, i.e. the 16 bp (base pair) sequence of
"gatagatagatagata" would represent 4 head-tail copies of the tetramer (groups of 4
nucleotides) "gata". The polymorphisms in STRs are due to the different number of copies of
the repeat element that can occur in a population of individuals.
D7S280
D7S280 is one of the 13 core CODIS STR genetic loci. This DNA is found on human chromosome
7. The DNA sequence of a representative allele of this locus is shown below. This sequence
comes from GenBank, a public DNA database. The tetrameric repeat sequence of D7S280 is
"gata". Different alleles of this locus have from 6 to 15 tandem repeats of the "gata" sequence.
How many tetrameric repeats are present in the DNA sequence shown below? Notice that one
of the tetrameric sequences is "gaca", rather than "gata".
1 aatttttgta ttttttttag agacggggtt tcaccatgtt ggtcaggctg actatggagt
61 tattttaagg ttaatatata taaagggtat gatagaacac ttgtcatagt ttagaacgaa
121 ctaacgatag atagatagat agatagatag atagatagat agatagatag atagacagat
181 tgatagtttt tttttatctc actaaatagt ctatagtaaa catttaatta ccaatatttg
241 gtgcaattct gtcaatgagg ataaatgtgg aatcgttata attcttaaga atatatattc
301 cctctgagtt tttgatacct cagattttaa ggcc
What are the 13 core CODIS loci?
A National DNA Databank
The Federal Bureau of Investigation (FBI) of the US has been a leader in developing DNA typing
technology for use in the identification of perpetrators of violent crime. In 1997, the FBI
announced the selection of 13 STR loci to constitute the core of the United States national
database, CODIS. All CODIS STRs are tetrameric repeat sequences. All forensic laboratories that
use the CODIS system can contribute to a national database. DNA analysts like Bob Blackett can
also attempt to match the DNA profile of crime scene evidence to DNA profiles already in the
database.
There are many advantages to the CODIS STR system:
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The CODIS system has been widely adopted by forensic DNA analysts
STR alleles can be rapidly determined using commercially available kits.
STR alleles are discrete, and behave according to known principles of population
genetics
The data are digital, and therefore ideally suited for computer databases
Laboratories worldwide are contributing to the analysis of STR allele frequency in
different human populations
STR profiles can be determined with very small amounts of DNA
A DNA Profile: The 13 CODIS STR loci
As part of his training and proficiency testing for DNA Profile analysis of STR (Short Tandem
Repeat) Polymorphisms, Forensic Scientist and DNA Analyst Bob Blackett created a DNA profile
on his own DNA. Here is Bob's DNA Profile for the 13 core Genetic Loci of the United States
national database, CODIS (Combined DNA Index System):
For each genetic locus, Bob has determined his "genotype", and the expected frequency of his
genotype at each locus in a representative population sample. For example, at the genetic locus
known as "D3S1358", Bob has the genotype of "15, 18". This genotype is shared by about 8.2%
of the population. By combining the frequency information for all 13 CODIS loci, Bob can
calculate that the frequency of his profile would be 1 in 7.7 quadrillion Caucasians (1 in 7.7
times 10 to the 15th power!
In Bob's forensic DNA work, he often compares the DNA profile of biological evidence from a
crime scene with a known reference sample from a victim or suspect. If any two samples have
matching genotypes at all 13 CODIS loci, it is a virtual certainty that the two DNA samples came
from the same individual (or an identical twin).
Methods of Analysis of STRs
We will assume that you have a basic understanding of the Polymerase Chain Reaction (PCR),
and gel electrophoresis, especially as applied to DNA sequence analysis. We will focus here on
the special features of PCR and gel electrophoresis as they are applied to STR characterization.
If you are unfamiliar with these techniques, you should still be able to complete this activity.
Methods in Analysis of the 13 CODIS STR loci
1. DNA extraction: DNA can be extracted from almost any human tissue. Buccal cells from
the inside of the cheek are most commonly used for paternity tests. Sources of DNA
found at a crime scene might include blood, semen, tissue from a deceased victim, cells
in a hair follicle, and even saliva. DNA extracted from items of evidence is compared to
DNA extracted from reference samples from known individuals.
2. PCR Amplification: DNA primers have been optimized to allow amplification of multiple
STR loci in a single reaction mixture. By carefully adjusting the distance of the primers
from the tetrameric repeat sequence, products from different loci will not overlap
during gel electrophoresis. In the partial results shown below, the three STRs D3S1358,
vWA, and FGA are being analyzed simultaneously. The lengths of the amplified DNAs are
shown by the scale from 100 bp to 280 bp at the top of the figure. The middle panels
with multiple peaks are reference standards with the known alleles for each STR locus.
Notice that the alleles for the three different loci do not overlap. The lower panel shows
the alleles for Bob Blackett's mother Norma for the D3S1358, vWA, and FGA loci.
Norma's alleles have been compared by computer to the refrence standards, and
labeled. To interpret this result, Norma's genotype is 15, 15 at the locus D3S1358, 14,
16 at vWA, and 24, 25 at FGA.
3. Detection of DNAs after PCR Amplification: The PCR primers in the commercial kits
used for STR analysis have fluorescent molecules covalently linked to the primer. To
extend the number of different loci that can be analyzed in a single PCR reaction,
multiple sets of primers with different "color" fluorescent labels are used. Following the
PCR reaction, internal DNA length standards are added to the reaction mixture and the
DNAs are separated by length in a capillary gel electrophoresis machine. As DNA peaks
elute from the gel they are detected with laser activation. The sequencing machines
used for allele separation and detection are the same type currently being used in the
Human Genome Sequencing project, with digital output that can be analyzed by special
computer software. In the AmpFLSTR™ Profiler Plus™ PCR Amplification Kit from Applied
Biosystems used by Bob Blackett, 9 STRs are analyzed by using three sets of primers.
Each set has a different colored fluorescent label. In the figure above, three sets of STRs
are represented by blue, three by green, and three by yellow (shown as black)
fluorescent peaks. The red peaks are the DNA size standards. Special computer software
is used to display the different colors as separate panels of data and determine the
exact length of the DNAs. A tenth marker called AMEL is used to distinguish male DNA
as X, Y or female DNA as X, X. A second kit, called Cofiler Plus, is used in a second PCR
reaction to amplify 4 additional STR loci, plus repeat some of the loci from the Profiler
Kit. The result from 2 PCR reactions is the analysis of the entire CODIS set of 13 STRs,
with overlap of some loci, and a test for the sex chromosomes. The results are obtained
as discrete, digital alleles determined from the exact size of the amplified products
compared to known standards.
Genetics of STR Inheritance
Since there are no phenotypes associated with the CODIS STR loci, understanding the genetics
of STR inheritance is simplified compared to other genetic problems. We need only consider the
genotypes of the parents and their offspring. The alleles of different STR loci are inherited like
any other Mendelian genetic markers. Diploid parents each pass on one of their two alleles to
their offspring according.
Here is brief review of the genetic concepts and terms important for understanding STR allele
inheritance.
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Allele. The different forms of a gene. Different STR repeat lengths represent different
alleles at a genetic locus, i.e. 8 and 9 are different alleles of the THO1 locus.
Locus. The position on a specific chromosome where the different alleles of a genetic
marker are located. The plural is loci.
Monohybrid Cross. Genetic cross involving parents differing in only one trait.
Inheritance of each of the 13 STR loci can be treated as a separate Monohybrid Cross.
Genotype. The genetic composition of the alleles at a locus. Since we are diploid, we
each have two alleles at each locus.
Homozygous. Both alleles at a locus are the same, i.e. Fred has a genotype of 29, 29 at
the D21S11 locus.
Heterozygous. Alleles at a locus are not the same, i.e. Normal has a genotype of 29, 31
at the D21S11 locus.
Multiple Allelic Series. Many different alleles at a locus, i.e. the known alleles at the
vWA locus are 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and 21.
Punnett Square. A diagram used to determine all possible genotypes that can occur in a
genetic cross. All of the diagrams on this page are Punnett Squares.
Here are some examples of the how STR data can be interpreted in a family DNA study. The
numbers outside the Punnett Squares are the parental alleles that can be present in the egg or
sperm of the parents. The numbers inside the squares are the genotypes possible for the
resulting children.
Case 1: If the genotypes of both parents are known, we use a Punnett Square to predict the
possible phenotypes of their offspring. Each child inherits one allele of a given locus from each
parent. Panel (a) - At the D21S11 locus, the children of Bob Blackett and wife Anne can have
four different genotypes. Son David is 28, 31. Daughter Katie is 29, 30. Panel (b) - Bob Blackett
inherited the 31 allele from his mother, Norma. Therefore the 29 allele is paternal. If Bob's
paternal allele was not 29, what would be your conclusion?
Case 2: In the genotypes of a mother and several children are known, it is often possible to
unambiguously predict the genotype of the father. In this case, Karen is the mother with a
genotype of 9, 9.3 at the THO1 locus. From the Punnett Square we can determine that the
paternal alleles of Tiffany, Melissa, and Amanda are 8, 9.3, and 9.3, respectively. Therefore,
their father Steve must have a genotype of 8, 9.3. If the three daughters had three different
paternal alleles, what would be your conclusion?
Case 3: Sometimes only one allele of the father can be predicted when the genotypes of a
mother and several children are known. In this example, the genotype of Karen, the mother, is
16, 17 at the D18S51 locus. The genotypes of the daughters are either 16 and 18 or 17 and 18.
In each case, Melissa, Tiffany, and Amanda inherited the 18 allele from their father, Steve. We
cannot determine if the genotype of Steve is homozygous, 18, 18 or 18, ? where the ? means
any other allele.
Case 4: Is it possible to determine parental genotypes when only the genotypes of their
children are known? Consider the case of Bob Blackett's 4 first cousins, Marilyn, Buddy, Dick
and Janet. Bob did not have DNA samples for their parents, Bud and Louise, who are both
deceased. In a real forensic case, Bud and Louise might represent "missing persons". In panel
(a) we can arrange the 3 known genotypes of the 4 children. In panel (b) we predict the only
two paternal genotypes for the parents that can account for the children. Note that we cannot
determine which genotype goes with which parent.
Case 5: A variation on Case 4 is when there are only two genotypes known for the children,
and both parental genotypes must be predicted. Panel (a) - Marilyn and Janet are 15, 16 at the
locus D3S1358. Buddy and Dick are 18, 18. Panel (b) - The only parental genotypes that can give
this result are 15, 18 and 16, 18. Once again, we cannot predict which parent as which
genotype.
Case 6: Sometimes the parental genotypes cannot be predicted unambiguously from the
genotypes of their children. Marilyn is 16, 17 at the locus vWA. Buddy, Dick, and Janet are 16,
18. What are the parental genotypes? Panel (a) - One interpretation is that the parents are 16,
18 and 16, 17. Panel (b) - Another possibility is that one parent is 17, 18 and the other is 16, ?,
where ? is any allele.
DNA Profile Frequency Calculations
Genotype Probability at any STR Locus
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Part of the work of forensic DNA analysis is the creation of population databases for the
STR loci studied.
Probability calculations are based on knowing allele frequencies for each STR locus for a
representative human population (and showning Hardy-Weinberg equilibrium for the
population by statistical tests).
Allele frequency is defined as the number of copies of the allele in a population divided
by the sum of all alleles in a population.
For a heterozygous individual, if the two alleles have frequencies of p and q in a
population, the probability (P) of an individual of having both alleles at a single locus is
P = 2pq
If an individual is homozygous for an allele with a frequency of p, the probability (P) of
the genotype is
P = p 2.
We saw earlier that Bob Blackett has the genotype 15, 18 at the locus D3S1358. In a
reference database of 200 U.S. Caucasians, the frequency of the alleles 15 and 18 was
0.2825 and 0.1450, respectively. The frequency of the 15, 18 genotype is therefore
P = 2 (0.2825) (0.1450) = .0819, or 8.2%.
Probability for a DNA profile of Multiple Loci
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If databases of allele frequency for different loci can be shown to be independently
inherited by appropriate statistical tests, the probability for the combined genotype can
be determined by the multiplication (product rule).
The probability (P) for a DNA profile is the product of the probability (P1, P2, ... Pn) for
each individual locus, i.e.
Profile Probability = (P1) (P2) ... (Pn)
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The probability can be an extremely low numbers when all 13 CODIS STR markers are
included in the DNA profile. As mentioned earlier, Bob Blackett calculated his own
profile probability at 1.3 times 10-16, or no more frequent than 1 in 7.7 quadrillion
individuals (7.7 million billion), which is more than a million times the population of the
planet.
Assignments
Create a Blackett Family Pedigree
The Blackett Family DNA Activity is largely a genetic study of the inheritance of alleles in an extended
family. Bob Blackett has tested DNA samples from himself and 13 other relatives. The first task of a
human geneticist is the creation of a family tree, or pedigree to help with the interpretation of
genotypes. From the following relationships, construct a pedigree for the Bob and his relatives.
Person
Bob
Anne
David
Katie
Fred
Norma
Karen
Steve
Tiffany
Melissa
Amanda
Louise
Bud
Buddy
Dick
Marilyn
Janet
Family Relationship
Our propositus
Wife
Son
Daughter
Father
Mother
Sister
Husband of Karen
Daughter of Karen and Steve
Daughter of Karen and Steve
Daughter of Karen and Steve
Sister of Fred; Bob's Aunt
Husband of Louise
Son of Bud and Louise
Son of Bud and Louise
Daughter of Bud and Louise
Daughter of Bud and Louise
Collecting STR DNA profile data
STR Data for the Blackett Family
These data are from the actual DNA analysis of the Blackett family members by Bob Blackett.
The tracings below show the genotypes for three of the 13 CODIS STR loci. In this activity, you
will record the data for use in the ensuing genetic analysis of the Blackett family. Data on the
other 10 loci will be provided later.
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Collect the data for Bob, Anne, David, Katie, Fred and Norma for the "Paternity Testing
with STR" Activity.
Collect the data for Karen, Tiffany, Melissa, and Amanda for the "DNA Profile of a
Missing Person" Activity.
You will not need to collect the results for Buddy, Dick, Marilyn and Janet. They are
provided for you to create your own activity, i.e. Can you make any conclusions about
Louise and Bud?
Paternity Testing with STR Data
In this activity, you will assume the role of a Human Geneticist in a DNA Paternity Testing
Laboratory. You have just obtained the DNA Profiles for Bob, Anne, David and Katie. You also
have information about Bob's parents, Fred and Norma. In your role as a Human Geneticist, it is
not essential that you know all of the laboratory techniques used to obtain the Blackett family
genotypes. Your work is based on understanding the principles of Mendelian Genetics as
applied to STR loci.
Here are your options:
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Go immediately to the questions below and interpret the data you have already
collected.
Review the principles of genetics needed for this activity
Use the data that we have collected for you.
Choose from among the following questions to test your understanding of human genetics.
1. Who are the parents of David and Katie? : Do all of the data you have collected on the
genotypes of Bob, Anne, Katie, and David support the conclusion that Bob and Anne are
the biological parents of David and Katie? You should justify your answer by reference
to the specific genotypes for the STR loci.
2. What is the genetic legacy of Fred and Norma? : The alleles that Bob passes on to his
children have in turn been inherited from Bob's parents, Fred and Norma. Identify the
alleles among the 13 CODIS STR loci in the genotypes of Katie and David that have been
unambiguously inherited from each of their paternal grandparents. Now identify any
additional alleles that might have been inherited from their paternal grandparents.
3. Genetic Diversity and Sexual Reproduction : Human geneticists are often asked why
children have not inherited a particular trait from their parents. As a human geneticist,
you know that one mechanism to insure genetic diversity is the independent assortment
of alleles of different loci during gamete (egg and sperm) production, i.e. Mendel's
Second Law of Genetics. To illustrate this important genetic principle, calculate how
many genotypes would be possible among the children of Bob and Anne for the
combined DNA profile from the D3S1358, vWA, and FGA. If you feel really ambitious,
now calculate the possible genotypes of the children of Bob and Anne for all 13 CODIS
STR loci.
4. How many genotypes are possible in a population for a three locus DNA Profile? : If
there are two alleles, A and B, at a genetic locus in a population, there are three possible
genotypes, namely AA, BB, and AB. If there are three alleles, A or B or C, there are six
possible genotypes, namely AA, BB, CC, AB, AC, and BC. For N different alleles, the total
possible genotypes are given by the following expression:
If we assume that the allele reference ladders from our data collection exercise
represent all possible alleles (a conservative estimate), how many genotypes are
possible in a population for the combined STR loci of D3S1358, vWA, and FGA?
5. How many genotypes are possible in a population for the combined CODIS 13 STR
loci? : If you feel really ambitious, you may wish to calculate the number of possible
genotypes considering all 13 CODIS STR markers. The table below shows the number of
alleles for each locus. Beware, the number will be very large.
DNA Profile of a "Missing Person"
In this activity you will assume the role of a forensic DNA analyst. Your task will be to determine
the DNA profile for a "missing person" from the analysis of close family members. DNA analysts
often have to recreate genotypes for those whose DNA is not readily available for analysis. A
recent case of great national interest was the identification of the remains of the Vietnam
soldier who had been interred in the Tomb of the Unknown Soldier.
Here are your options:
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Go immediately to the questions below and interpret the data you have already
collected.
Review the principles of genetics needed for this activity
Skip the data collection, and use the data that we have collected for you for Question
#1.
Completed data for Buddy, Dick, Marilyn, and Janet in for Question #2.
1. What is Steve's Genotype? : In our activity, we obtained data for Karen and her three
daughters, Tiffany, Melissa, and Amanda. Bob Blackett has not yet had the opportunity
to test the DNA of Steve, so Steve can play the role of the "missing person" in our
activity. Determine Steve's genotype at the 13 CODIS STR loci. Indicate whether there is
an unambiguous genotype where both alleles are known, or some uncertainty about
both paternal alleles.
2. What are the Genotypes of Bud and Louise? : What happens when we have two
missing people? Human geneticists are often asked to determine if adult children in the
same family all have the same biological parents. Demonstrate that all of the genetic
information for the children of Bud and Louise is consistent with all 4 having the same
two parents.
DNA Profile Frequency Calculations
In this activity, you can calculate the probability for some of the DNA profiles you have been
studying. The following sets of data are tables of allele frequency for the three STR loci
D3S1358, vWA, and FGA for a combined, Caucasian population. The frequency data come from
the web site of the Royal Canadian Mounted Police.
1. What is the Probability for a 3-Locus DNA profile? : Based on a population
database of Caucasians developed by Bob Blackett and colleagues in Arizona,
Bob can calculate the genotype frequency of his combined profile for the three
STR loci D3S1358, vWA, and FGA to be 6 x 10-5. Compare this frequency with the
frequency you calculate from the Royal Canadian Mounted Police data. For help
with this calculation, review the DNA Profile Frequency Calculation earlier in the
packet (page 15).
2. Check your answers. : As an alternative to doing all of the arithmetic yourself,
you can calculate a profile's Random Match Probability using the RCMP on-line
calculator at http://www.csfs.ca/pplus/profiler.htm
DATA PAGES: