Title HG CL 5 BASIC OF INHERITANCE.pdf ✅

Eg : Fragile X syndrome - FMR 1 – mutation expansion of CGG trinucleotide repeats Normal 5-44 copies Gray zone 45-54 copies (instability) Premutation 55-200 copies Full mutation >200 copies 4. New mutation - Never assume that an isolated case (which is dominantly inherited) is the result of a new mutation – reduced penetrance OR gonadal mosaicism - Proportion of cases resulting from a new mutation will be directly related to the degree to which the disease interferes with reproduction (genetic fitness) - Common cause of the appearance of a genetic disease in a person with no previous family history of the disorder. - The recurrence risk for the person’s siblings is very low, but the recurrence risk for the person’s offspring may be substantially increased. - Apert syndrome: almost all new mutations, as compared to Huntington disease 5. Codominance - Two allelic traits that are both expressed in the heterozygous state - Eg ; individuals with blood group AB - Demonstrate both A and B blood group substances on the RBCs