Transcript PowerPoint Notes

A family history of a genetic condition
Pages 1-3 & 6-9 taken from Paul Billiet at the following website:
saburchill.com/IBbiology/.../images/05PEDIGREE CHARTS.ppt
What is a pedigree chart?
 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.
Studying human genetics
 You cannot make humans of different types breed
together
 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
Sex on a Pedigree
 Males
 Females
Connecting Lines
 Marriage – horizontal line
between two people
 Siblings – horizontal line
above boxes
 Twins


Fraternal
Identical
Children are listed from youngest to oldest (left to right)
Symbols used in pedigree charts
Normal male
Affected male
Normal female
Affected female
or
autosomal carrier (heterozygote )
x-linked carrier
or
deceased
Organizing the pedigree chart
 A pedigree chart of a family showing 20
individuals
Organizing the pedigree chart
 Generations are identified by Roman numerals
I
II
III
IV
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
Reading a Pedigree Chart
 Autosomal or x-linked trait?
 If the affected are mostly males then the trait is x-linked
 If the affected is a fairly even ratio between males and
females then the trait is autosomal
Autosomal or X-linked?
Autosomal
Determining Dominant or
Recessive Trait?
 If the disorder is dominant one of the parents must
have the disorder
 If the disorder is recessive then neither of the parents
HAS to have the trait because they are heterozygous.
However one of both may have the disorder
Dominant or recessive?
Dominant
Dominant or Recessive?
Recessive
Some times carriers are not listed as a half filled in square/circle. You must
interpret the pedigree
Remember….
you must READ and INTERPRET the pedigree.