Severe Acute Respiratory
Syndrome (SARS)
H1N1 流感病毒
流感的启示……
流行时间
发源地
流行病毒
流行地区
死亡人数
1918年-1919年
美国/
法国
H1N1
三元重组病毒
全球
4000万-1亿
1957年
中国
H2N2
二元重组病毒
全球
全球100万
（美国6.98万）
1968年
香港
H3N2
二元重组病毒
全球
美国3.38万
2003年
中国
H5N1
高致病性禽流感
亚洲
病死率61%
2009年
北美
H1N1
三元重组病毒
全球
病死率1.22%
问题
1、为什么每一次大流行的流感病毒的类型都不一样？
2、为什么如此猖狂和恐怖的流感病毒不能像天花病毒一样被“消
灭”？为什么不能通过接种疫苗进行有效的预防？
血凝素（HA）
神经氨酸酶（NA），
SARS的S蛋白质和M蛋白质的变异点位达到31个，这说明
SARS病毒具有极强的变异能力，这意味着研究SARS疫苗可
能会同研究流感疫苗一样困难重重……
Chapter 10
Gene Mutation
OUTLINE
1、What Are Mutations?
2、 Features of Gene Mutantion
3、Consequences of Mutations
4、What Causes Mutations?
5、How to Detect the Gene Mutation?
1、What Are Mutations?

★ Any heritable change in the DNA（RNA） sequence of an organism
is a mutation.

★ Mutations can be divided into three main types
1. Chromosome mutations（染色体突变）
2. Genome mutations（基因组突变）
3. gene mutations（基因突变）Relatively small changes in DNA structure
that occur within a particular gene
★ Gene mutation（基因突变）: changes in one or a few nucleotides.
★ point mutation(点突变) are mutations of a single nucleotide.Includes
the deletion, insertion, or substitution in a gene.（碱基的增加及缺失、
碱基替换）
替换
增加及缺失

A transition(转换) is a change of a pyrimidine (C, T) to another
pyrimidine or a purine (A, G) to another purine

A transversion(颠换) is a change of a pyrimidine to a purine or
vice versa
转换和
颠换的
相互关
系示意
图
Mutations may also involve the addition or deletion of
short sequences of DNA
5’ AACGCTAGATC 3’
3’ TTGCG ATCTAG 5’
5’ AACGCTC 3’
3’ TTGCGAG 5’
Deletion of four base pairs
5’ AACGCTAGATC 3’
3’ TTGCGATCTAG 5’
5’ AACAGTCGCTAGATC 3’
3’ TTGTCAGCGATCTAG 5’
Addition of four base pairs
Mutations Due to Trinucleotide Repeats（dynamic mutation）
2、 Features of Gene Mutantion

Mutations happen regularly

Mutation rate

Forward & backward(or reverse) mutation

Multiple orientations

Beneficial & deleterious

Mutation similarity between the related species
Mutations happen regularly
The size of the patch
will depend on the
timing of the mutation
The earlier the mutation, the
larger the patch
An individual who has
somatic regions that are
genotypically different
from each other is called a
genetic mosaic
Therefore, the
mutation can be
passed on to
future generations
Therefore, the
mutation cannot
be passed on to
future generations
Mutation rate
The frequency with which a particular mutation
appears in a population.
Forward & backward(or reverse) mutation
(正突变&回复突变)
forward
A
a
reverse
通常从一个野生型基因变成突变性的频率总是高于
回复突变率，如何解释？
一突变型回复成野生型，可能机制是什么？（预习基
因重组）
a1
Multiple orientations
（多向性）
A
a2
a3
Beneficial & deleterious
beneficial
Harmful
Almost all mutations are neutral
Some terms

lethal mutation（致死突变）: Mutation that eventually
results in the death of an organism carrying the mutation.

neutral mutation（中性突变）: A mutation that has no
selective advantage or disadvantage.

conditional mutation（条件突变）: A mutation that is only
expressed under certain environmental conditions.
Mutation similarity between the related species（突变的平行性）
+
3、Consequences of Mutations
Mutations in the coding sequence of a structural gene
(can have various effects on the polypeptide)
Mutations in Non-coding Sequences
(affect gene expression)
3、Consequences of Mutations- coding sequence
3、Consequences of Mutations- coding sequence
3、Consequences of Mutations- coding sequence
☆Silent mutations (or silent) mutation（同义突变）: base
substitutions that do not alter the amino acid sequence of the polypeptide.
☆ Missense mutations(错义突变) are those base substitutions in
which an amino acid change does occur.
☆ Nonsense mutations （无义突变）: are those base
substitutions
that change a normal codon to a termination codon.
☆ Frameshift mutations （移码突变）: involve the addition or
deletion of nucleotides in multiples of one or two.
如果你所研究的基因发生了突变，你将如何从遗传学
角度判断他是错义突变、无义突变还是移码突变？
3、Consequences of Mutations- Noncoding sequence
为什么操纵子区（oprator）和启动子(promoter)突变总是
顺式显性和反式隐形突变？而编码阻抑蛋白基因突变，则是顺式还是反式
显性呢？
4、What Causes Mutations?

Mutations can occur spontaneously or be induced

Spontaneous mutations(自发突变)
 Result from abnormalities in cellular/biological processes
 for example： Errors in DNA replication

Induced mutations （诱发突变）
 Caused by environmental agents

Agents that are known to alter DNA structure are termed
mutagens

These can be chemical or physical agents
Summary
1、What Are Mutations?
2、 Features of Gene Mutantion
3、Consequences of Mutations
4、What Causes Mutations?