Transcript Pedigree Basics

What does pedigree mean?
Pedigree: a diagram that traces one trait
through several generations of a family
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
3
How many girls? ___
2
How many boys? ___
mom
daughter #1
dad
daughter #2
son
mom
dad
oldest
daughter #1
youngest
daughter #2
son
A horizontal line connecting two
shapes represents a cross/marriage.
mom
dad
Example #2
How many crosses/marriages?
2
A
C
B
D
E
F
G
A vertical line extending down from a
marriage/cross represents that the
couple has children.
mom
dad
A
C
B
D
questions…
E
F
G
Example #3
A
C
How many couples
have children?
B
D
H
H
G
E
F
M
J
N
K
L
O
?
P
Q
R
S
T
4
How do you show twins?
A
C
B
D
E
F
How do you show traits? Shading
( shaded = recessive )
RR
Rr
rr
mutation
**A pedigree chart follows one trait.
Rr
mom
RR
dad
R = tongue roller
r = non-roller
Rr
son
Rr
daughter
RR
daughter
R
R
R
RR
RR
r
Rr
Rr
A
C
B
D
G
E
F
M
Practice
questions…
J
N
P
HH
K
L
O
Q
R
S
T
What is wrong
with this
pedigree chart?
This offspring
cannot receive 2
recessive genes.
This offspring cannot
receive 2 dominant genes.
This offspring
cannot receive 2
recessive genes.
What are
possible
genotypes for
individual W?
W
R
r
R
RR
Rr
r
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.
Aa
If you have 2 recessive genes, you
are sick with the disease. (you are
“affected”)
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
4
3
Granddaughter, carrier, 3rd generation, older sibling
Grandson, carrier, 3rd generation, middle sibling
rr
Rr
1
7
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 Answers
4
1.
How many children did the first generation have?
2.
How many girls did the first generation have?
3.
Describe individual Y.
A female carrier/hybrid
4.
Describe individual Z.
A male carrier/hybrid
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.
10.
11.
3
1
rr
Rr
7
Shows the dominant trait, but can pass the
What is a carrier?
recessive gene on to offspring.
How many kids did W and his wife have?
2
U
Who is older, U or V?
It comes first left to right
How do you know?
Goals of Pedigree Analysis
• 1. Determine the mode of inheritance:
dominant, recessive, partial dominance, sexlinked, 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 Charts
 Is
it Autosomal or X-linked?
Answer
 Autosomal
Interpreting a Pedigree Chart
2.
Determine whether the disorder is
dominant or recessive.
– If the disorder is dominant, one of
the parents must have the
disorder.
– If the disorder is recessive, neither
parent has to have the disorder
because they can be heterozygous.
Example of Pedigree Charts
 Dominant
or Recessive?
Answer
 Dominant
Example of Pedigree Charts
 Dominant
or Recessive?
Answer
 Recessive
Summary
 Pedigrees
are family trees that
explain your genetic history.
 Pedigrees are used to find out the
probability of a child having a
disorder in a particular family.
 To begin to interpret a pedigree,
determine if the disease or condition
is autosomal or X-linked and
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 Fibrosis