细胞生物学英文课件-7.1 染色体畸变(结构改变)

ab c ab c
d e f g ef g d ef
重复的遗传学效应
重复对基因平衡的影响：扰乱了生物体本身基因固有的平 衡体系，影响了个体的生活力。
有害程度：取决于重复区段基因数量的多少及其重要性， 与缺失相比，有害性相对较小，但若重复区段过长，往往 使个体致死。
对育性的影响：重复杂合体一般败育，重复纯合体会产生 “剂量效应(dosage effect)”。
• In a karyotype, the chromosomes are arranged by pairs: alterations in chromosome size (structure) or number are seen here.
Normal Human Karyotype
A normal human cell contains 46 chromosomes: 22 pairs of autosomes（常染色体）, and two sex chromosomes.
Common Structural Abnormalities
(3) Duplications(重复): gain of genetic material (4) Translocation(易位): no change in the amount of genetic
material (if balanced)
Chromosomal Abnormalities (染色体畸变)
Introduction
• Cytogenetics (细胞遗传学) is the field of study involving examination of the genetic material of the cells.
Characteristics
o Round, moon-shaped face o “Cry of the cat” o Varying degrees of mental
retardation o Low set ears
Cri du chat syndrome
(二)Duplication的细胞学特征
(2)顶端缺失 有丝分裂出现因断裂—融合→双着丝粒染色体——后期染色 体桥。 减数分裂联会时，有未配对的游离区段。
(3)中间缺失 减数分裂染色体联会时形成缺失环。
注意：较小的缺失往往并不表现出明显的细胞学特征；缺失纯 合体减数分裂过程也无明显的细胞学特征。
缺失的细胞学特征
断裂(breakage)—融合(fusion)—桥(bridge)
• The genetic material (DNA) is contained in chromosomes. Each organism has a characteristic number and arrangement of chromosomes.
• A karyotype （核型） is a photograph of the chromosomes at metaphase, when they are most easily seen.
缺失杂合体的假显性现象
来自百度文库
Micro Deletions（教材下册p8 ）
• Some genetic syndromes are caused by very small deletions in the chromosome in human.
• These syndromes have been useful in locating genes involved in specific processes.
Chromosomal Abnormalities
• Chromosomal abnormalities can be of two types.
(1) Structural(结构) abnormalities are caused by breaks in the chromosome being incorrectly repaired. “Ends” of broken chromosomes are very unstable in a cell.
顶端缺失的形成(断裂) 复制 姊妹染色单体顶端断
头连接(融合) 有丝分裂后期桥(桥)
新的断裂
玉米缺失杂合体粗线期缺失环
果蝇唾腺染色体的缺失环
缺失的遗传学效应
(1)缺失的后果 打破了基因的连锁平衡，破坏了基因间的互作关系，基因所 控制的生物功能或性状可能丧失或异常。
(2)缺失的危害程度 取决于缺失区段的大小、缺失区段所含基因的多少、缺失基 因的重要程度、染色体倍性水平。 缺失纯合体——致死或半致死 缺失杂合体——缺失区段较长时，生活力差、配子(尤其是 花粉)败育或育性降低；缺失区段较小时，可能会造成假显 性现象或其它异常现象(猫叫综合症)。
(2) Numerical(数目) abnormalities are caused by gain or loss of chromosomes.
Common Structural Abnormalities
(1) Deletions (缺失)：loss of genetic material (2) Inversions (倒位): no change in the amount of genetic material
(一) Deletions
①顶端缺失(Terminal Deletions )：指缺失 的区段位于染色体某臂的外端。
②中间缺失(Interstitial Deletions )：指缺 失的区段位于染色体某臂的中间。
缺失的细胞学鉴定
(1)无着丝粒断片：最初发生缺失的细胞在分裂时可见落后染 色体——无着丝粒断片，
• “Cri du Chat” (cry of the cat) is caused by a small deletion at the tip of chromosome 5 in human.
5p－ Syndrome (Cat Cry syndrome)
1 in 50000 newborns