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 individualThey can be used to study the transmission

of a hereditary conditionThey are particularly useful when there are

large families and a good family record over several generations.

Studying human geneticsYou cannot make humans of different types

breed togetherPedigree 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 PedigreeMales

Females

Connecting LinesMarriage – horizontal

line between two peopleSiblings – horizontal line

above boxesTwins

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 chartGenerations are identified by Roman

numerals

I

II

III

IV

Organizing the pedigree chartIndividuals in each generation are identified by Arabic

numerals numbered from the leftTherefore the affected individuals are II3, IV2 and IV3

I

II

III

IV

Reading a Pedigree ChartAutosomal 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.