© 2006 Jones & Bartlett Publishers Fig Conventional symbols used in depicting human pedigrees. propositusperson initiating the study expressivityvariation in phenotype penetranceif phenotype genotype

© 2006 Jones & Bartlett Publishers Pedigrees can be used to follow transmission routes (who got it from whom) Can sometimes be used to determine type of transmission (autosomal or X-linked) (dominant or recessive) New (spontaneous) mutations would be difficult to interpret

++ p Autosomal recessive: both sexes affected equally most affected people have unaffected parents about 1/4 of children of a pair of carriers would be affected if two affected individuals reproduce all offspring will be affected

Autosomal dominant: both sexes affected equally affected people have at least one affected parent about 1/2 of children of a affected person would be affected (most affected people are heterozygous)

X-linked (sex-linked) recessive: males show trait more than females in families: often grandfather to grandson transmission all affected females have affected fathers

X-linked (sex-linked) dominant: more common in females than males every affected person has at least on affected parent daughters of affected males will be affected females pass it on to half of their children (assuming they are heterozygous)

Most human genetic disease are “rare.” If too many unrelated people have to be carriers… …probably the wrong mode of inheritance.

X-linkedorautosomal ? X d X d Y X D Y X D X d recessiveordominant

i iiiii autosomal recessiveordominant

autosomal dominant

blood typing H antigen A antigen B antigen H antigen h antigen A transferase B transferase no transferase ii IA_IA_ IB_IB_ can’t make H antigen Bombay phenotype (hh) (HH) no A or B antigen no A or B or H antigen no B antigen no A antigen