Human Pedigrees

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Transcript Human Pedigrees

Human Genetic Pedigrees
Tracking your own family traits
What is a Genetic Pedigree?
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A genetic pedigree is an easy way to track your family
traits. It looks like a family tree, but also contains
information about your genetic history.
A doctor or geneticist might draw one for your family if
you had a family history of a particular disease. With
this information they could see how the disease is
inherited and calculate your probability of passing on
the disease to your future children.
Before you continue, for your warm up, brainstorm with
your partner on what you think a genetic pedigree might
look like.
Assignment Table of Contents
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Assignment 1: Notes
– Genetic pedigree notations
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Generations
Symbols
Marriage Lines
Children Lines
Self Check1
– More notations
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Remarriages
Adoptions
Twins
– Tracking Traits
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Phenotype notation
Genotype determination
Determining trait inheritance
(dominant / recessive)
Self Check 2
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Assignment 2: Quiz
– Quiz on Ms. Yoneda’s
Family
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Assignment 3: Your
Genetic Family Pedigree
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Part A
Part B
Part C
Part D
Rubric
Assignment 1: Notes
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You and your partner are to go through the following
pages to learn about
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What a genetic pedigree is
How to read a genetic pedigree
How to read and encode genetic traits in a pedigree
How to draw a human genetic pedigree
Read carefully and make sure both you and your partner
understand before you move on, because you will be
tested on your understanding of a genetic pedigree at
the end of this assignment.
For assignment 1 you will not need to turn in your
notes, but you will be graded on how well you and your
partner are working together to learn the information.
Table of Contents
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Generations
I
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1
2
– Notice it restarts at 1 every new
generation.
– When possible, older siblings are on
the left and younger siblings are on the
right in descending order.
II
2
1
3
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III
1
This is an example of a family tree
showing 3 generations of family
members.
The roman numerals (in red) on the
left indicate the generation each
person belongs to.
Each individual in a generation is
then numbered (in green).
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Using this system, the individual at
the bottom of this pedigree is III:1.
Age does not matter in determining
which generation an individual is
in. Children are always in the next
generation after their parents.
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Symbols
I
1
2
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II
2
1
III
1
3
Each of the individuals
indicated by a circle is a woman
and each of the squares
represents a male family
member.
We now know that individual
III:1 is a male.
Occasionally, the sex of an
individual may not be known.
Common reasons for this would
be, miscarriages or early death,
babies given up for adoption, a
child that has not been born yet,
or distant family members.
 These individuals can be noted by
using a diamond symbol
instead of a square or circle.
“Marriage Lines”
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I
1
2
II
2
1
III
1
3
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The lines highlighted in red
indicate individuals that
have had children together.
Even though we call them
“marriage lines” it does not
matter if they are married,
were married, or were
never married.
It is important to realize
that time has no meaning
on a genetic pedigree,
therefore we do not usually
indicate if someone has
died or been divorced.
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“Children Lines”
I
1
2
II
The lines highlighted in red are
“children lines”
– The marriage line that they are
connected to from above indicates who
gave them their genetic traits rather than
who raised them.
– If a couple has more than one child
together then we split the child line as
the green highlighted line shows. More
siblings would simply require a longer
line with more lines coming down from
it.
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2
1
III
1
3
Thus II:2 and II:3 are children of I:1 and
I:2, but II:1 married into the family and
has different parents. We also know that
II:2 is older than his sister (read left to
right). However, we don’t know
anything about the relative age of II:1
even though she is on the left since she
married into the family.
 Be careful when you draw siblings to
show lines coming in from the top rather
than using a “marriage line” to connect
them.
Self Check 1
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I
1
2
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II
2
1
III
1
3
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For each of the individuals in
the family tree to the left,
indicate how they are related to
I:1. Be specific (for example,
use grandson or granddaughter
instead of grandchild.)
Write your answers on your
paper and label this section self
check 1.
When you and your partner are
done check your answers on the
next page.
Self Check 1
Answers
Wife
I
1
Daughter In-law
II
Son
(oldest child)
2
1
III
2
Daughter
(youngest child)
3
Grandson
1
Table of Contents
More Pedigree Notations
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Since every family is unique, the
information on the previous pages may not
cover all families. The following are some
commonly needed notations in drawing
family trees.
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This is an example of how to show
a parent who has had children with
more than one person. It can also
be used to show remarriage. It
does NOT mean that they are
married to more than one person at
the same time. Remember, time
has no meaning in a pedigree.
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In this example, II:1 and II:2 are
half brother and sister. They share
the same mother, but different
fathers. Typically, the older
sibling is still put first, but this is
not always possible.
Remarriages
Half Siblings
I
1
2
3
II
1
2
Remarriages
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Step Siblings
I
II
1
2
1
Step brothers and sisters are not
related by blood. In the example
below I:2 and I:3 each had
children from a prior relationship.
This means that II:1 and II:3 are
step brothers since they don’t
share the same biological parents.
3
4
2
3
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Table of Contents
If your family has a situation with a more
complex marriage/sibling situation, ask and I
will show you how to draw it.
Adoptions
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I
1
2
II
1
Adoptions are also fairly
common, but need to be
shown differently from
biological children since they
did not inherit their genetic
information from the parents
who raised them.
– The red line shows how to use
dashed “children lines” to
denote a child that is not
related biologically (adopted).
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Table of Contents
In this example, the couple
adopted a son.
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Twins
I
1
2
II
1
2
3
4
Table of Contents
Twins are another fairly common
occurrence. However, there are
two kinds and from a genetic
standpoint it is very important to
know the difference.
– In the case of identical twins, the two
siblings have the same DNA. To
show this we split the sibling line at
an angle. The red highlighted line is
an example of this.
– In the case of fraternal twins,
although born at the same time, the
siblings are no more related than any
other siblings. Thus, they are drawn
the same as any siblings. The green
highlighted lines show this.
Tracking Traits
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So far we have only looked at how to draw family
relationships. To make a family tree into a genetic
pedigree we need to be able to track a particular
trait.
– When we track traits we first put phenotypes into our
pedigrees. We then use these phenotypes to determine
possible types of inheritance of the trait and their
corresponding genotypes.
Step 1: Tracking
Phenotypes
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I
1
2
II
2
1
III
3
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Regardless of what the trait is,
geneticists shade in individuals
that have the phenotype of the
trait you are interested in
tracking.
For example, in this pedigree, 4
family members have the trait
of interest: I:1, II:1, II:3, and
III:1. In this case the key at the
bottom tells us that these four
individuals are nearsighted,
which is a known recessive trait
1
= nearsighted
= normal
Table of Contents
Step 2:
Recessive
Traits
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I
1
2
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II
2
1
III
1
= nearsighted (n)
= normal (N)
3
The next step is to put in the
genotypes of each family
member.
The way to start putting in
genotypes is to start with the
recessive trait and put in all
their genotypes first.
In this case, since nearsighted is
known to be a recessive trait we
start with all the shaded
individuals. Remember, a
recessive phenotype means that
individual has two recessive
genes. (Click to put in the
genotypes)
Step 2:
Recessive
Traits
1
2
nn
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nn
2
1
III
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nn
I
II
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nn
1
= nearsighted (n)
= normal (N)
3
The next step is to put in the
genotypes of each family
member.
The way to start putting in
genotypes is to start with the
recessive trait and put in all
their genotypes first.
In this case, since nearsighted is
known to be a recessive trait we
start with all the shaded
individuals. Remember, a
recessive phenotype means that
individual has two recessive
genes.
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Step 3:
Dominant Traits
nn
I
1
II
nn
nn
2
1
III
2
nn
1
= nearsighted (n)
= normal (N)
3
The next step is to put in the
known N gene for all
individuals with a dominant
phenotype. (Remember
someone showing the dominant
trait can be homozygous
dominant or heterozygous.)
(Click to put in the genotypes)
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Step 3:
Dominant Traits
nn
I
1
II
III
N
The next step is to put in the
known N gene for all
individuals with a dominant
phenotype. (Remember
someone showing the dominant
trait can be homozygous
dominant or heterozygous.)
2
nn
N
1
2
nn
1
= nearsighted (n)
= normal (N)
nn
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3
Sometimes we can tell who
should be NN and who is Nn if
we look at their parents or their
children’s genotypes. However,
sometimes one still cannot tell
and we put in N_, where the
line represents either N or n.
Step 4:
Determining the
2nd gene
nn
I
1
II
III
N
2
nn
N
1
2
nn
1
= nearsighted (n)
= normal (N)
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In this case look at I:2. We
know that she had a recessive
daughter II:3. II:3 has nn so she
had to have gotten one from
both parents. This means that
I:2 must have a little n as her
second gene. (Click to put in the
genotypes)
nn
3
Step 4:
Determining the
2nd gene
nn
I
1
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Nn
2
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II
III
nn
N
1
2
nn
1
= nearsighted (n)
= normal (N)
nn
3
In this case look at I:2. We
know that she had a recessive
daughter II:3. II:3 has nn so she
had to have gotten one from
both parents. This means that
I:2 must have a little n as her
second gene.
In the case of II:2 we can also
tell their second gene is a little n
by looking at either his father or
at his son who both have nn
genes. (Click to put in the genotypes)
Step 4:
Determining the
2nd gene
nn
I
1
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Nn
2
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II
III
nn
Nn
1
2
nn
1
nn
3
In this case look at I:2. We
know that she had a recessive
daughter II:3. II:3 has nn so she
had to have gotten one from
both parents. This means that
I:2 must have a little n as her
second gene.
In the case of II:2 we can also
tell their second gene is a little n
by looking at either his father or
at his son who both have nn
genes.
– Remember each parent always
passes one of their two genes to
every child they have. This also
means that every child receives
one gene from each parent.
= nearsighted (n)
Table of Contents
= normal (N)
Determining trait inheritance:
dominant or recessive
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Sometimes you need to determine if a trait is
dominant or recessive just by looking at the
pedigree. In general assume dominant if you
cannot find the…
Recessive clue: Anytime that a child has a trait
and neither parent has it, that trait must be
recessive! (Using the pedigree shown here, can
you and your partner explain why? Hint: put in
the genotypes.)
Table of Contents
Self Check 2: Trait Inheritance
& Genotypes
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c)
A: For each of the three
pedigrees determine if the
black trait is dominant or
recessive.
B: Then determine the
genotypes of the following
individuals (Use A & a).
– a) II:3, II:4, III:4, III:6
– b) III:3, III:4, IV:1, IV:2
– c) I:1, I:2, II:4
Self Check 2 Answers: Trait
Inheritance & Genotypes
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A:
– a) recessive
– b) recessive
– c) dominant
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c)
B: Then determine the
genotypes of the following
individuals.
– a) Aa, Aa, aa, A_
– b) Aa, Aa, aa, A_
– c) Aa, aa, aa
Table of Contents
Assignment 2: Quiz
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On the next page is Ms. Yoneda’s Genetic Family Tree
for tongue rolling.
For your quiz, you will need to be able to read the
pedigree and be able to determine
– Family relationships
– Genotypes of family members
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If you’re not ready, go back to the table of contents,
review, and try the self-quizzes again
Table of Contents
When you think that you are ready, you and your partner
may take the quiz together.
Once you are done, make sure both partners names are
on it and turn it in.
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Ms. Yoneda is individual III:4
Work with your partner to answer the following questions.
1.
2.
3.
4.
5.
6.
7.
8.
How many generations are shown?
How is Ms. Yoneda related to I:1
How are III:6 and III:7 related to each other?
How are III:6 and III:7 related to Ms. Yoneda?
How is III:5 related to Ms. Yoneda?
How is IV:2 related to Ms. Yoneda?
How is II:1 related to Ms. Yoneda?
Put in the genotypes for all individuals shown. (Including ? Individuals)
?
?
Key:
White shading = cannot roll (r)
Blue shading = can roll (R )
? = unknown phenotype
?
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Assignment 3: Part A
Now that you understand how to draw and analyze a basic genetic
pedigree. You will use this information to draw your own family
pedigree using the following guidelines.
– You only need to draw one side of your family (either your mother’s or your
father’s NOT both)
– Include at least 3 generations of family members
– Although “marriage lines” typically are only used for couples that have had
children, you may use them to show any married or unmarried couples that are
part of the family, regardless if they have had children together or not.
 Hint: When you draw your own pedigree, start with your parents as the first two
individuals. Then add in generations before and after your parents.
– When you are done, have your partner check your rough draft. (Partners you are
checking for errors AND if they meet all the above requirements. If it passes
both of these, write Part A and sign their rough draft). Once it is signed,
proceed to part B.
Table of Contents
Assignment 3: Part B
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Now you are ready to track a trait in your
family. Earlier in this unit you were asked
to interview your family members to find
out everyone’s phenotype for a particular
trait.
Make a key and use shading to show the
phenotypes in your family for this trait.
Table of Contents
Assignment 3: Part C
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Now you need to determine if the trait you tracked
in your family is dominant or recessive.
Be sure to look for family groups where the trait
skips generations. Remember if a child shows the
phenotype and the parents do not, then it is a
recessive trait.
Before you go on, go over your reasons why you
determined it was a dominant or recessive trait
with your partner and make sure they agree with
you.
Table of Contents
Assignment 3: Part D
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Choose a letter to represent your dominant and recessive
genes and record it on your key.
Then go through your family and put in the genotypes of
all members that have a known phenotype. Don’t forget
that genotypes always have 2 letters. Use a line to
represent an unknown second letter.
Before you do your final draft, have two classmates
check your work. (Have your classmate check for all
the requirements on the next page and look for any
errors you may have made. If they agree that you have
completed everything correctly, have them write Part D
and sign.)
Table of Contents
Assignment 3: Rubric
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At least 3 generations shown and indicated with roman numerals on
your pedigree
Phenotypes shown for family members (as many as possible)
Probable genotypes for all family members that have a known
phenotype
Label at least yourself on your family tree. For all others either give
a name (first) or label with correct number notation
A key is given for phenotypes and corresponding allele (letter)
Name, date, and period is on the back
Final Draft:
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Must use a ruler
Table of Contents
Done in ink (or on the computer)
Done on non-lined paper (computer paper)
Rough draft with 3 signatures attached (1 for part A, 2 for part D)
Learning Objectives
Learn how to read, draw, and analyze the inheritance
pattern of a human genetic pedigree
State Standards:
1.
2.
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2: Mutation and sexual reproduction lead to genetic variation in a
population
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2c: random chromosome segregation explains the probability that a
particular allele will be in a gamete
2e: approximately half of an individual's DNA sequence comes from each
parent
2g: predict possible combinations of alleles in a zygote from the genetic
makeup of the parents
3: A multicellular organism develops from a single zygote, and
its phenotype depends on its genotype, which is established at
fertilization
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3a: predict the probable outcome of phenotypes in a genetic cross from the
genotypes of the parents and mode of inheritance
3c: predict the probable mode of inheritance from a pedigree diagram
using phenotypes