Medical Genetics
04 基因突变的分子
细胞生物学效应
cellular effects of gene mutation
Medical Genetics
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,
Medical Genetics
Medical Genetics
When a gene contains a mutation,
the protein encoded by that gene is
likely to be abnormal,
Medical Genetics
Medical Genetics
Medical Genetics
2,Somatic versus germline mutations
Gene mutations can be either
inherited from a parent or acquired,
Medical Genetics
Medical Genetics
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 offspring's body cells,
Medical Genetics
The fact that every cell contains
the gene change makes it possible to
use cheek cells or a blood sample for
gene testing,
Medical Genetics
Medical Genetics
Acquired mutations are changes
in DNA that develop throughout a
person's lifetime,
Medical Genetics
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,
Medical Genetics
Medical Genetics
3,Types of mutation effects
(1) Morphological mutations
give rise to altered forms,
Medical Genetics
Medical Genetics
Medical Genetics
(2) Lethal mutations
result in nonviable organisms,
Medical Genetics
(3) Conditional mutations
gives a mutant phenotype under
restrictive conditions (environmental)
and causes a wild type phenotype
under permissive conditions,
Medical Genetics
(4) Biochemical mutations
result in the inability to carry out
a specific biochemical pathway
(inborn errors of metabolism),
Medical Genetics
(5) Loss-of-function (null) mutations
(lof)
result in no gene function are
usually recessive although some
haploinsufficient dominant "lof"
mutations exist,
Medical Genetics
Medical Genetics
A common lof mutation is the
partial loss-of-function or "leaky"
mutation,
Medical Genetics
Medical Genetics
(6) Gain-of-function mutation (gof)
result in altered gene function
that act as a dominant allele and
produces a novel phenotype,
Medical Genetics