What does pedigree mean?

Pedigree: a diagram that traces one trait through several generations of a familyX

What are they used for?

• Pedigree charts show a record of the family of an individual

• They can be used to study the transmission of a hereditary condition

• They are particularly useful when there are large families and a good family record over several generations.

© 2007 Paul Billiet ODWS

Studying human genetics

• Pedigree charts offer an ethical way of studying human genetics

• Today genetic engineering has new tools to offer doctors studying genetic diseases

• A genetic counsellor will still use pedigree charts to help determine the distribution of a disease in an affected family

© 2007 Paul Billiet ODWS

= female = male

Example #1 How many girls? ___How many boys? ___

mom dad

sondaughter #1

32

daughter #2

mom dad

oldest youngest

sondaughter #1 daughter #2

A horizontal line connecting two shapes represents a cross/marriage.

mom dad

Example #2 How many crosses/marriages?

2A B

C D E F

G

A vertical line extending down from a marriage/cross represents that the couple has children.

mom dad

A B

C D E F

G

questions…

Example #3 How many couples have children?

4

A B

C D E F

HG H

KJ L

M N O

P RQ S T

?

A B

C D E F

How do you show twins?

How do you show traits?

Shading

RR Rr mutationrr

**A pedigree chart follows one trait.

( shaded = recessive )

Rrmom

RRdad

Rrson

Rrdaughter

R

r

R R

RR RR

Rr Rr

RRdaughter

R = tongue rollerr = non-roller

A B

C D E F

HG H

KJ L

M N O

P RQ S T

Practice questions…

What is wrong with this

pedigree chart?

This offspring cannot receive 2 recessive genes.

This offspring cannot receive 2 recessive genes.

This offspring cannot receive 2 dominant genes.

What are possible

genotypes for individual W?

W

R

r

R r

RR Rr

Rr rr

W could be RR (no shading) or Rr (half-shaded) or rr (all shaded).

Pedigree charts help to trace genetic diseases. Most genetic diseases are a recessive gene.

If you have 1 recessive, you are a carrier, but you are not sick.

If you have 2 recessive genes, you are sick with the disease. (you are “affected”)

Aa

aa

Organising the pedigree chart

– Generations are identified by Roman numerals

I

II

III

IV

© 2007 Paul Billiet ODWS

Organizing the pedigree chart• Individuals in each generation are identified by Arabic

numerals numbered from the left• Therefore the affected individuals are II3, IV2 and IV3

I

II

III

IV© 2007 Paul Billiet ODWS

43

Granddaughter, carrier, 3rd generation, older sibling

Grandson, carrier, 3rd generation, middle sibling

1

7

rrRr

A person that carries one copy of the disease gene, but it is masked by the dominant trait. (hybrid)

2

U

U is further left. This makes U older than V

Genetic Pedigree Answers1. How many children did the first generation have?

2. How many girls did the first generation have?

3. Describe individual Y.

4. Describe individual Z.

5. How many children and grandchildren have the disease?

6. What is the genotype of X? Use the letter R/r.

7. What is the genotype of Y? Use the letter R/r.

8. How many children and grandchildren are carriers for the disease?

9. What is a carrier?

10. How many kids did W and his wife have?

11. Who is older, U or V?

How do you know?

43

A female carrier/hybrid

A male carrier/hybrid

Shows the dominant trait, but can pass the recessive gene on to offspring.

2

It comes first left to rightU

7

rr

Rr

1

Goals of Pedigree Analysis

• 1. Determine the mode of inheritance: dominant, recessive, partial dominance, sex-linked, autosomal, mitochondrial, maternal effect.

• 2. Determine the probability of an affected offspring for a given cross.

Sex-Linked Traits

• What determines if a baby is a male or female? Recall that you have 23 pairs of chromosomes—and one of those pairs is the sex chromosomes . Everyone has two sex chromosomes. Your sex chromosomes can be X or Y. Females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY).

• If a baby inherits an X chromosome from the father and an X chromosome from the mother, what will be the child’s sex?

• The baby will have two X chromosomes, so it will be female. If the father’s sperm carries the Y chromosome, the child will be male. Notice that a mother can only pass on an X chromosome, so the sex of the baby is determined by the father. The father has a 50 percent chance of passing on the Y or X chromosome, so there is a 50 percent chance that a child will be male, and there is a 50 percent chance a child will be female.

Y-Linked Inheritance• We will now look at how

various kinds of traits are inherited from a pedigree point of view.

• Traits on the Y chromosome are only found in males, never in females.

• The father’s traits are passed to all sons.

• Dominance is irrelevant: there is only 1 copy of each Y-linked gene (hemizygous).

Sex-Linked Trait/Y-Linked

One example of a sex-linked trait is red-green colorblindness. People with this type of colorblindness cannot tell the difference between red and green. They often see these colors as shades of brown ( Figure below ). Boys are much more likely to be

colorblind than girls ( Table ). This is because colorblindness is a sex-linked, recessive trait.

Interpreting a Pedigree Chart

1. Determine if the pedigree chart shows an autosomal or X-linked disease.

– If most of the males in the pedigree are affected the disorder is X-linked

– If it is a 50/50 ratio between men and women the disorder is autosomal.

Example of Pedigree ChartsExample of Pedigree Charts

Is it Autosomal or X-linked?Is it Autosomal or X-linked?

AnswerAnswer

AutosomalAutosomal

Interpreting a Pedigree ChartInterpreting a Pedigree Chart

2.2. Determine whether the disorder is Determine whether the disorder is dominant or recessive.dominant or recessive.

– If the disorder is dominant, one of If the disorder is dominant, one of the parents must have the disorder.the parents must have the disorder.

– If the disorder is recessive, neither If the disorder is recessive, neither parent has to have the disorder parent has to have the disorder because they can be heterozygous.because they can be heterozygous.

Example of Pedigree ChartsExample of Pedigree Charts

Dominant or Recessive?Dominant or Recessive?

AnswerAnswer

DominantDominant

Example of Pedigree ChartsExample of Pedigree Charts

Dominant or Recessive?Dominant or Recessive?

AnswerAnswer

RecessiveRecessive

SummarySummary

Pedigrees are family trees that Pedigrees are family trees that explain your genetic history.explain your genetic history.

Pedigrees are used to find out the Pedigrees are used to find out the probability of a child having a probability of a child having a disorder in a particular family.disorder in a particular family.

To begin to interpret a pedigree, To begin to interpret a pedigree, determine if the disease or condition determine if the disease or condition is autosomal or X-linked and is autosomal or X-linked and dominant or recessive.dominant or recessive.

Cystic fibrosis (CF)

also known as mucoviscidosis, is a genetic disorder that affects mostly

the lungs but also the pancreas, liver, kidneys and intestines.

 Long-term issues include difficulty breathing and coughing up sputum as a result of frequent lung infections. Other symptoms include sinus infections, poor growth, clubbing of the fingers and toes, and infertility in males among others. Different people may have different degrees of symptoms.

CF is an autosomal recessive disorder.

Pedigree Chart -Cystic FibrosisPedigree Chart -Cystic Fibrosis