Human Genetic Pedigrees

Tracking your own family traits

What is a Genetic Pedigree? 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 neighbor what you think a genetic pedigree might look like. Sketch an example of one for horns in a Purple People Eater

Generations

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).– 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.

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.

I

II

III

1

2

2

31

1

Symbols 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.

I

II

III

1

2

2

31

1

“Marriage Lines” 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.

I

II

III

1

2

2

31

1

“Children Lines”

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.

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.

1

2

2

31

1

I

II

III

Self Check 1 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.

I

II

III

1

2

2

31

1

Self Check 1Answers

WifeI

II

III

Daughter(youngest child)

1

2

2

3

Daughter In-law

Grandson

1

1

Son(oldest child)

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More Pedigree Notations

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.

RemarriagesHalf Siblings

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.

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.

I

II

1

2

2 3

1

RemarriagesStep Siblings

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.

If your family has a situation with a more complex marriage/sibling situation, ask and I will show you how to draw it.

I

II

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1

2

2 3

1

4

3

Adoptions 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).

In this example, the couple adopted a son.

I

II

1 2

1

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Twins

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.

I

II

1 2

1 2 3 4

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Tracking Traits

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

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

I

II

III

1

2

2

31

1

= nearsighted= normal Table of Contents

Step 2: Recessive

Traits

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)

I

II

III

1

2

2

31

1

= nearsighted (n)= normal (N)

Step 2: Recessive

Traits

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.

nnI

II

III

nn

1

2

2

3

nn

nn

1

1

= nearsighted (n)= normal (N)

Step 3: Dominant Traits

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)

nnI

II

III

nn

1

2

2

3

nn

nn

1

1

= nearsighted (n)= normal (N)

Step 3: Dominant Traits

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.)

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.

NnnI

II

III

nn

1

2

2

3

nn

nn

1

1

N

= nearsighted (n)= normal (N)

Step 4: Determining the

2nd gene

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)

NnnI

II

III

nn

1

2

2

3

nn

nn

1

1

N

= nearsighted (n)= normal (N)

Step 4: Determining the

2nd gene

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)

NnnnI

II

III

nn

1

2

2

3

nn

nn

1

1

N

= nearsighted (n)= normal (N)

Step 4: Determining the

2nd gene

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.

NnnnI

II

III

nn

1

2

2

3

nn

nn

1

1

Nn

= nearsighted (n)= normal (N)

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Determining trait inheritance: dominant or recessive

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.)

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Self Check 2: Trait Inheritance & Genotypes

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

c)

Self Check 2 Answers: Trait Inheritance & Genotypes

A: – a) recessive– b) recessive– c) dominant

B: Then determine the genotypes of the following individuals.– a) Aa, Aa, aa, A_– b) Aa, Aa, aa, A_– c) Aa, aa, aac)

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Assignment 2: Quiz 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

If you’re not ready, go back to the table of contents, review, and try the self-quizzes again

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. How many generations are shown?2. How is Ms. Yoneda related to I:13. How are III:6 and III:7 related to each other?4. How are III:6 and III:7 related to Ms. Yoneda?5. How is III:5 related to Ms. Yoneda?6. How is IV:2 related to Ms. Yoneda?7. How is II:1 related to Ms. Yoneda?8. Put in the genotypes for all individuals shown. (Including ? Individuals)

Key:White shading = cannot roll (r)Blue shading = can roll (R )? = unknown phenotype

?

? ?

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.

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Assignment 3: Part B

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.

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Assignment 3: Part C

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.

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Assignment 3: Part D

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.)

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Assignment 3: Rubric 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:

– Must use a ruler– 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)

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