Pedigree Basics!

PEDIGREEs

They are like family trees
They show: 1) How traits are transmitted (causes of diseases)

2) Predictions of the probabilities of having an affected child
3) If the trait is dominant or recessive
4) If the gene is autosome or X-linked

PEDIGREE SYMBOLS

Common patterns

PEDIGREE EXAMPLE
NOTE: The generations are given Roman Numerals which are listed on the left hand side of the pedigree.
Tt
Tt
i
2.
2.
3.
3.
2.
1.
2.
iI
tt
T-
T-
1. The coloured female has to be “tt”.
2. All the ones that are not coloured have to have a “T”.
3. If one of the offspring is “tt” then it got one “t” from the mother and one “t” from the father.
4. The genes for the other offspring cannot be figured out so you put a dash.

PEDIGREE PRACTISE PROBLEM
The ability to roll your tongue is determined by the dominant gene (T). In the following pedigree, affected individuals CAN roll their tongue. Based on the pedigree, determine the genotype for each individual.
i
Ii
IIi

2
1
3
4
i
tt
tt
T
Tt
9
10
6
7
8
5
Ii
tt
tt
tt
Tt
Tt
Tt
12
13
14
17
15
16
11
IIi
T
T
Tt
Tt
tt
tt
tt
All the non-filled in males and females have to be “tt”.
All the filled in males and females have to have a “T”.
Number 1 must be “Tt” because it has an offspring that is “tt”.
Number 7 must be “Tt” because it got the “T” from the father so it can only get “t” from its mother.
Number 8 must be “Tt” because it got the “T” from the mother and so it can only get “t” from its father.
Number 9 must be “Tt” because it got the “T” from the mother and so it can only get “t” from its father.
Number 16 and 17 must be “T” because they got the “T” from their father so they can only get “t” from their mother.
Number 4, 14, and 15 remain unknown.
tt
T
Tt

PEDIGREE X- LINKAGE PRACTISE PROBLEM
This pedigree represents the inheritance of the gene that causes albinism. A and B represent a couple that had five children, including C and E. C married D and had four children. E married F and had five children, including G. Figure out the genotypes of the following: A, B, C, D, E, F, and G.
A
B
i
C
D
E
F
Ii
G
IIi

A
B
i
Aa
Aa
C
D
E
F
Ii
aa
Aa
Aa
A-
G
IIi
Aa
Use A to represent the dominant allele, and a to represent the recessive allele.
1. E is aa because it is coloured in and therefore it has been affected.
2. A and B must be Aabecause they must both give an a in order to make E and they both must have an A to give to all the other children that are not affected.
3. C and D must be Aabecause they must both give an a in order to make one of their offspring affected, and an A to give all the other children that are not affected.
4. F must have an A because it has offspring that are not affected.
5. G has to be Aabecause it gets the a from the mother and the A from the father.
6. Whether F is Aaor AAis unknown so we leave it at A-.

Click here for practice problems with answers!
Click here for practise problems that are challenging
Both of the pedigree practice questions were taken from the worksheet Pedigrees and Pedigree Practise Problems.
However, the answer steps were personally created.