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

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.

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.

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.

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

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

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

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.

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.

Tongue rolling

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).

Tongue rolling

Tongue rolling rr rr rr rr rr

Tongue rolling All non-rollers must be genotype rr

Tongue rolling rr rr rr rr rr

Tongue rolling rr Rr Rr rr Rr Rr Rr rr 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.

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

Albinism

Albinism aa Aa Aa Aa Aa Aa Aa Aa aa aa aa aa

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.

Polydactyly

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

Brachydactyly