染色體畸變結(jié)構(gòu)改變-展示頁
2025-05-10 22:58本頁面
【正文】 t 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. Normal Human Karyotype A normal human cell contains 46 chromosomes: 22 pairs of autosomes（常染色體） , and two sex chromosomes. Chromosomal Abnormalities ? Chromosomal abnormalities can be of two types. (1) Structural(結(jié)構(gòu) ) abnormalities are caused by breaks in the chromosome being incorrectly repaired. “Ends” of broken chromosomes are very unstable in a cell. (2) Numerical(數(shù)目 ) abnormalities are caused by gain or loss of chromosomes. Common Structural Abnormalities (1) Deletions (缺失 )： loss of geic material (2) Inversions (倒位 ): no change in the amount of geic material Common Structural Abnormalities (3) Duplications(重復(fù) ): gain of geic material (4) Translocation(易位 ): no change in the amount of geic material (if balanced) (一 ) Deletions ①頂端缺失 (Terminal Deletions )： 指缺失的區(qū)段位于染色體某臂的外端。 ②中間缺失 (Interstitial Deletions )： 指缺失的區(qū)段位于染色體某臂 的中間。 減數(shù)分裂聯(lián)會時，有未配對的游離區(qū)段。 注意：較小的缺失往往并不表現(xiàn)出明顯的細(xì)胞學(xué)特征；缺失純合體減數(shù)分裂過程也無明顯的細(xì)胞學(xué)特征。 (2)缺失的危害程度 取決于缺失區(qū)段的大小、缺失區(qū)段所含基因的多少、缺失基因的重要程度、染色體倍性水平。 缺失的 遺傳學(xué)效應(yīng) 缺失雜合體的假顯性現(xiàn)象 Micro Deletions（ 教材下冊 p8 ） ? Some geic syndromes are caused by very small deletions in the chromosome in human. ? These syndromes have been useful in locating genes involved in specific processes.
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