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

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 (if there are also reliable family records over several generations). © 2016 Paul Billiet ODWS

Studying human genetics 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

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

Symbols used in pedigree charts Identical Twins Normal male Affected male Normal female Affected female Marriage. FraternalTwins © 2016 Paul Billiet ODWS

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

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

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

Tongue rolling © 2016 Paul Billiet ODWS

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

Tongue rolling © 2016 Paul Billiet ODWS

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

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

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

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

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

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

Albinism © 2016 Paul Billiet ODWS

Albinism aa Aa Aa Aa Aa Aa Aa Aa aa aa aa aa © 2016 Paul Billiet ODWS

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

Polydactyly © 2016 Paul Billiet ODWS

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

Brachydactyly © 2016 Paul Billiet ODWS