医学遗传学人类染色体畸变.ppt

医学遗传学人类染色体畸变
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Any type of change in the chromosome structure or number (deficiencies, duplications, translocations, inversions, etc.).
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Although it can be a mechanism for enhancing genetic diversity, such alterations are usually fatal or ill-adaptive, especially in animals.
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1. factors inducing chromosome aberration
A. Ionizing radiation
Ionizing radiation produces rearrangements of the genome.
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When irradiation occurs during the G0/G1 phase of the cell cycle, large-scale rearrangements appear as exchange-type chromosome aberrations at the next mitosis. Such aberrations can alter cellular phenotypes, and are important in various areas of biology:
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Medical and public-health applications include perinatal diagnostics characterization of specific cancer types, carcinogenesis risk estimation, radiation biodosimetry and radiotherapeutic treatment planning.
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Analyzing chromosome aberrations helps characterize repair/misrepair pathways involved in the processing of DNA damage. Ionizing radiation has some unique features as a probe of such pathways. Compared to other genotoxic agents, it produces copious quantities of DNA double strand breaks (DSBs), and its timing can be controlled more accurately.
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Moreover, initial radiation damage has a discrete, stochastic character that can be modulated by using different kinds of radiation (. a -particles versus x-rays) having different ionization densities.
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The spectrum of different radiation-induced chromosome aberrations is informative about the geometry of chromosomes during interphase, and vice versa.
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