Chapter 8 - Chapter 8 Cytogenetics study of normal and...

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Chapter 8 chrom mutation = chrom aberration – variations from wild-type condition in chrom structure/number o arise spontanteously or can be induced experimentally o detected by genetic analysis – observing changes in linkage arrangements of genes o can be detected under microscope during mitosis/meiosis in eukaryotes variations in chrom. structure o intro begin w/ 1+ breaks in chrom. if w/in gene, function of gene can be lost broken ends have no telomeres that prevent degredation; “sticky” ends can adhere to other broken chrom. ends polytene chrom. – special chrom that consist of chromatid bundles resulting from endoreplication (repeated cycles of chrom duplication w/out nuclear or cell division) found in certain tissues, like salivary gland of insects can be 1000 times size of corresponding chrom. at meiosis or in the nuclei of ordinary somatic cells easily detectable under the microscope homologous chrom. are tightly paired, so observed # of polytene chrom./cell is reduced to ½ the diploid # of chrom joined at centromeres by protinaceous chromocenter characteristic binding patterns easily seen when chrom are stained o ex: Giemsa shows G bands (darker areas of staining vs interbands; each ~30 kbp; each located in the identical posisiton of a particular chrom in all individuals of the same species o deletion – missing a part of chrom caused by breaks due to heat/radiation/viruses/chemicals/transposable elements/errors in recomb deletion mutations can’t revert to wild-type b/c chrom segment is missing consequences heterozygous for deletion may be normal, unless homolog contains recessive genes w/ deleterious effects o pseudodominance - unmasked recessive alleles if it involves loss of centromere acentric chrom, usu lost during meiosis possible lethal consequences heterozygotes usually some some genetic disorder, homozygotes tend to be lethal
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can visualize as a distortion of a band/interband/unpaired loops during meiosis can be used for deletion mapping ex: cri-du-chat: deletion of short arm of chrom 5 mental retardation, physical abrnomalities, cry like the mew of a cat Prader-Willi syndrome: deletion of long arm of chrom. 15, in
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This note was uploaded on 02/09/2010 for the course BIOL 3301 taught by Professor Hannig/miller during the Spring '10 term at Dallas.

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Chapter 8 - Chapter 8 Cytogenetics study of normal and...

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