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
AUTOSOMAL
RECESSIVE
INHERITANCE
AUTOSOMAL
DOMINANT
INHERITANCE
X-LINKED
RECESSIVE
INHERITANCE
PARENT
Both must be
One parent is
heterozygous or affected
homozygous
recessive
There is not
father to son
transmission
GENERATION
Trait may skip
generations
Trait does not
skip
generations
Trait skips
generations
OFFSPRING
Males and
females are
affected equally
Only half of the
children are
affected
(males and
females are
affected
equally)
It affects more
males than
females
PEDIGREE EXAMPLE
i
NOTE: The
generations are
given Roman
Numerals which are
listed on the left
hand side of the
pedigree.
iI
The coloured female has to be “tt”.
All the ones that are not coloured have to have a “T”.
If one of the offspring is “tt” then it got one “t” from the mother and one “t” from the
father.
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
1
i
5
Ii
IIi
1.
2.
3.
4.
5.
6.
7.
8.
11
2
6
12
3
7
13
4
9
8
14
15
16
10
17
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.