1. PEDIGREE CHARTS A family history of a genetic condition
Aim: How can we begin to read and understand pedigree charts?

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.

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.

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.

5. Organising the pedigree chart
A pedigree chart of a family showing 20 individuals.

6. Organising the pedigree chart
Generations are identified by Roman numerals. I II
III IV

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

8. Some pedigree terms to know.
Autosomal recessive: Involves a recessive allele on a non-sex chromosome.
Autosomal Dominant: Involves a dominant allele on a non-sex chromosome.

9. Some pedigree terms to know
X-linked recessive: Involves a recessive allele on the X-chromosome.
X-linked dominant: Involves a dominant allele on the X-chromosome.
Y-linked: Involves an allele on the Y-chromosome.

10. Tongue rolling

11. 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).

12. Tongue rolling

13. Tongue rolling rr rr rr rr rr

14. Tongue rolling
All non-rollers must be genotype rr

15. Tongue rolling rr rr rr rr rr

16. Tongue rolling rr Rr Rr rr Rr Rr Rr rr rr Rr rr

17. 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.

18. Tongue rolling
Unfortunately people can learn to roll their tongues too.

19. Albinism

20. Albinism aa Aa Aa Aa Aa Aa Aa Aa aa aa aa aa

21. 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.

22. Polydactyly

23. Dominant conditions
If two affected parents have an unaffected child the allele for the affected condition is dominant.

24. Brachydactyly