Complication that affect inheritance of single gene disease

1. Variable expression ---some severely affected some mildly affected. Ex;hereditary hemochromatosis, neurofibromatosis type 1
2. incomplete penetrance--genotype same phenotype not display.EX: heriditary retinoblastoma
3. pleiotrphy- single mutate affect mutipe organ part. EX: marfan syndrome,cystic fibrosis. 
4. locus heterogenity-- the same disease phenotype can be cause b y mutation at diferent loci.Often involved mutation in coding of multi-chain molecules. EX: osteogenic imperfecta,brittle bone disease,mutation in collagen boes,chromosomes 7/12.
5. new mutation
6. delay age of onset
7. anticipation-- most recent generation develop disease at earier age with greater severity
   
   EX: myotonic dystrophy,fragile x syndrome ,hungtinton disease and freidrech-ataxia.
8. imprinting-the gene from the other parent is inactivated by methylationj during gametogenesis.