1. A family history of a genetic condition
PEDIGREE CHARTS
A family history of a genetic condition
© 2016 Paul Billiet ODWS

2. What is a pedigree chart?
A record of the family of an individual
Used to study the transmission of a hereditary condition
Useful when there are large families and a there is a good family record over several generations.
© 2016 Paul Billiet ODWS

3. 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.
© 2016 Paul Billiet ODWS

4. Symbols used in pedigree charts
A marriage with five children, two daughters and three sons. The middle son is affected by the condition
Eldest child  Youngest child
Normal male
Affected male
Normal female
Affected female
Marriage.
© 2016 Paul Billiet ODWS

5. Organising the pedigree chart
A pedigree chart of a family showing 20 individuals.
© 2016 Paul Billiet ODWS

6. Organising the pedigree chart
Generations are identified by Roman numerals. I II
III IV
© 2016 Paul Billiet ODWS

7. Organising 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
© 2016 Paul Billiet ODWS

8. Tongue rolling
© 2016 Paul Billiet ODWS

9. If two affected individuals give rise to an unaffected child the affected condition is dominant
So roller allele is dominant (R) and non-roller allele is recessive (r).
© 2016 Paul Billiet ODWS

10. Tongue rolling
© 2016 Paul Billiet ODWS

11. Tongue rolling rr rr rr rr rr
© 2016 Paul Billiet ODWS

12. Tongue rolling All non-rollers must be genotype rr
© 2016 Paul Billiet ODWS

13. Tongue rolling rr rr rr rr rr
© 2016 Paul Billiet ODWS

14. Tongue rolling rr Rr Rr Rr rr Rr Rr rr rr Rr rr
© 2016 Paul Billiet ODWS

15. Tongue rolling
If one of the parents is a roller and the other is a non-roller all the roller children must be heterozygous rollers (Rr)
If a roller parent has a non-roller child the parent must be heterozygous.
© 2016 Paul Billiet ODWS

16. Tongue rolling
Unfortunately people can learn to roll their tongues too.
© 2016 Paul Billiet ODWS

17. Albinism
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18. Albinism aa Aa Aa Aa Aa Aa Aa Aa aa aa aa aa
© 2016 Paul Billiet ODWS

19. Albinism - a recessive condition
If two unaffected individuals give rise to an affected child, the allele for the affected condition is recessive
The unaffected parents are carriers (heterozygous)
Thus recessive conditions can skip several generations
Inbreeding increases the chance of carriers producing an affected child.
© 2016 Paul Billiet ODWS

20. Polydactyly
© 2016 Paul Billiet ODWS

21. Dominant conditions
If two affected parents have an unaffected child the allele for the affected condition is dominant.
© 2016 Paul Billiet ODWS

22. Brachydactyly
© 2016 Paul Billiet ODWS