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 and a there is a good family record over several generations. © 2016 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. © 2016 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 middle son is affected by the condition Eldest child Youngest child © 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 nonroller 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 © 2016 Paul Billiet ODWS Rr Rr rr 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