医学遗传学 04基因突变的分子机制eng v.ppt

04 基因突变的分子细胞生物学效应 cellular effects of gene mutation,1.Genes can be mutated in many ways,The most common gene change involves a single base mismatch-a misspelling-placing the wrong base in the DNA.At other times,a single base may be dropped or added.And sometimes large pieces of DNA are mistakenly repeated or deleted.,When a gene contains a mutation,the protein encoded by that gene is likely to be abnormal.,2.Somatic versus germline mutations,Gene mutations can be either inherited from a parent or acquired.,Hereditary mutations are carried in the DNA of the reproductive cells.When reproductive cells containing mutations combine to produce offspring,the mutation will be in all of the offsprings body cells.,The fact that every cell contains the gene change makes it possible to use cheek cells or a blood sample for gene testing.,Acquired mutations are changes in DNA that develop throughout a persons lifetime.,Although mistakes occur in DNA all the time,especially during cell division,a cell has the remarkable ability to fix them.But if DNA repair mechanisms fail,mutations can be passed along to future copies of the altered cell.,3.Types of mutation effects,(1)Morphological mutations give rise to altered forms.,(2)Lethal mutations result in nonviable organisms.,(3)Conditional mutations gives a mutant phenotype under restrictive conditions(environmental)and causes a wild type phenotype under permissive conditions.,(4)Biochemical mutations result in the inability to carry out a specific biochemical pathway(inborn errors of metabolism).,(5)Loss-of-function(null)mutations(lof)result in no gene function are usually recessive although some haploinsufficient dominant lof mutations exist.,A common lof mutation is the partial loss-of-function or leaky mutation.,(6)Gain-of-function mutation(gof)result in altered gene function that act as a dominant allele and produces a novel phenotype.,