染色体畸变(结构改变).ppt

Chromosomal Abnormalities
(染色体畸变)
染色体畸变(结构改变)
Cytogenetics (细胞遗传学) is the field of study involving examination of the genetic material of the cells.
The genetic material (DNA) is contained in chromosomes.
Each organism has a characteristic number and arrangement of chromosomes.
Introduction
染色体畸变(结构改变)
A karyotype （核型） is a photograph of the chromosomes at metaphase, when they are most easily seen.
In a karyotype, the chromosomes are arranged by pairs: alterations in chromosome size (structure) or number are seen here.
染色体畸变(结构改变)
Normal Human Karyotype
A normal human cell contains 46 chromosomes: 22 pairs of autosomes（常染色体）, and two sex chromosomes.
染色体畸变(结构改变)
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.

(2) Numerical(数目) abnormalities are caused by gain or loss of chromosomes.
染色体畸变(结构改变)
Common Structural Abnormalities
(1) Deletions (缺失)：loss of genetic material
(2) Inversions (倒位): no change in the amount of genetic material
染色体畸变(结构改变)
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)
染色体畸变(结构改变)
(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。
染色体畸变(结构改变)
染色体畸变(结构改变)
(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，
(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。
缺失的细胞学鉴定
染色体畸变(结构改变)