文档介绍：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, trogression.
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B. chemical mutagen
A kind of substances, such as drugs or toxins ,that causes chromosomal aberrations of living organisms, or increase the rate of mutation.
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2. chromosomal aberrations
A. chromosome numerical aberration
Numerical aberration is a change in the number of chromosomes from the normal number characteristic of the human beings.
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(1) Euploidy is the condition of having a normal number of structurally normal chromosomes.
Euploid human females have 46 chromosomes (44 autosomes and two X chromosomes).
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Polyploidy is a multiple of the haploid chromosome number (n) other than the diploid number (., 3n, 4n and so on).
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(2) Aneuploidy is the condition of having less than or more than the normal diploid number of chromosomes, and is the most frequently observed type of cytogenetic abnormality.
In other words, it is any deviation from euploidy, although many authors restrict use of this term to conditions in which only a small number of chromosomes are missing or added.
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Generally, aneuploidy is recognized as a small deviation from euploidy for the simple reason that major deviations are rarely compatible with survival, and such individuals usually die prenatally.
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The two most commonly observed forms of aneuploidy are monosomy and trisomy.
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Monosomy is lack of one of a pair of chromosomes. An individual having only one chromosome 6 is said to have monosomy 6. A common monosomy seen in many species is X chromosome monosomy, also known as Turner's syndrome. Monosomy is most commonly lethal during prenatal development.
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Trisomy is having three chromosomes of a particular type. A common autosomal trisomy in humans in Down syndrome, or trisomy 21, in which