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BIO207H5 (42)
Chapter 16

Chapter 16 - Textbook Notes.doc

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Nicole Myers

Chapter16VariationsinChromosomeStructureandNumberChromosomal mutations or chromosomal aberrationsare variations from the normal wildtype condition in chromosome structure or chromosome numberCan occur spontaneously or can be induced by treatment with chemicals or radiationContribute to spontaneously aborted pregnancies and still births as well as to some forms of cancerVariationsinChromosomeStructure4 common types of chromosomal mutations involve changes in chromosome structure deletions and duplications both of which involve a change in the amount of DNA on a chromosome inversions which involve a change in the orientation of a chromosomal segment and translocations which involve a change in the location of a chromosomal segment All occur with one or more breaks in the chromosomethis results in a loss of function for that geneThese broken ends sticky ends remain without the specialized sequences found at the ends of chromosomes telomeres that prevent their degradation Examining sticky ends can help analyze the formation of the types of mutationsPolytene chromosomesspecial kinds of chromosomes found in certain tissues Consist of chromatid bundles resulting from repeated cycles of chromosome duplication without nuclear or cell division a process called endoreduplication In each polytene chromosome the homologous chromosomes are tightly paired therefore the observed number of polytene chromosomes per cell is reduced to half the diploid number of chromosomes They are joined together at their centromeres by a proteinanceous structure called the chromocenterAs a result of intimate pairing characteristic banding patterns are easily seen when the chromosomes are stained DeletionA deletion is a chromosomal mutation in which part of a chromosome is missing It starts where breaks occur in chromosomes which can be induced by agents like heat radiation viruses chemicals and transposable elements Because a segment of chromosome is missing deletion mutations cannot revert to the wild type state
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