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PEDIGREE CHARTS

A family history of a genetic condition

© 2007 Paul Billiet ODWS

Warm-up1. What is the definition of allele?

2. What is the difference between genotype and phenotype?

3. Write an example of a heterozygous pair.

4. Are dominant alleles capitalized or lower-case?

5. Two people are heterozygous for brown hair, which is dominant to blonde hair. Set up the punnett square and solve. What is the chance that the offspring will be blonde?

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.

© 2007 Paul Billiet ODWS

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

© 2007 Paul Billiet ODWS

Symbols used in pedigree charts

Normal male Affected male Normal female Affected female Marriage

A marriage with five children, two daughters and three sons. The eldest son is affected by the condition.

Eldest child Youngest child

© 2007 Paul Billiet ODWS

More Symbols used in pedigree charts

Organising the pedigree chart

A pedigree chart of a family showing 20 individuals

© 2007 Paul Billiet ODWS

Organising the pedigree chart

Generations are identified by Roman numerals

I

II

III

IV

© 2007 Paul Billiet ODWS

Example: Color Blindness

Pedigree for Sickle-Cell Anemia

Observations 1. How many generations are represented in the chart for sickle-cell anemia? __________ 2. How many carriers of the sickle-cell trait are in each generation? _________________ 3. How many people in the family were born with sickle-cell anemia? _______________ 4. From with parent did the second-generation children inherit the sickle-cell gene? ____ 5. In which generation did sickle-cell anemia first show? __________________________ Conclusions 1. What can you determine about a family using a pedigree chart? (Be specific) ________ ________________________________________________________________________