染色体畸变结构改变.pptx

Chromosomal Abnormalities
(染色体畸变)
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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
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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.
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Normal Human Karyotype
A normal human cell contains 46 chromosomes: 22 pairs of autosomes（常染色体）, and two sex chromosomes.
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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.
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Common Structural Abnormalities
(1) Deletions (缺失)：loss of genetic material
(2) Inversions (倒位): no change in the amount of genetic material
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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)
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(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。
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(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
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