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Unformatted text preview: Final Review Chapter 12: Chromosomal Aberrancies- Chromosomal aberrancies : cells having abnormalities in the structure and/or number of their chromosomes- Mosaic (somatic aberrancy) : when a person has different groups of cells in various parts of his body which have a different chromosomal make-up than do the cells adjacent to those groups o Occurs as a result of chromosome lag (see below): Half of the cells are normal, the other half have 45 chromosomes o Occurs as a result of nondisjunction: Half of the cells have 45 chromosomes, the other half have 47 o Can occur at any division- Aberrancies occurring in meiosis I: o Deletions : the process by which a chromosome loses a piece of itself Occurs when a piece of a chromosome breaks off and is lost from the nucleus Occurs during crossing-over: when one chromatid ends up bigger than the other, the smaller piece was deleted, and the bigger piece was duplicated Occurs as a result of chromosome lag : when one chromosome lags behind the others in moving towards opposite sides of the cell, so that it is left out during cytokenesis and deleted Embryo usually does not survive Cri-du-chat syndrome (#5 chromosome deletion): children are mentally retarded, and sound like cats when they cry #18 chromosome deletion: causes mental retardation and short stature o Translocations : when a doubling-chromosome breaks and a piece of it attaches to another chromosome Every translocation is accompanied by a deletion on behalf of the broken chromosome Causes: Chromosome 21 attaching to chromosome 14: symptoms similar to Down Syndrome Williams Syndrome (small deletion in #7): causes mental retardation and remarkable abilities w/language and music Activation of cancer-causing genes- Aberrancies in Meiosis II: o Nondisjunctions : process whereby the two chromatids in a doubling chromosome do not separate as they normally would during the appropriate stage of Meiosis Chromatids eventually divide, producing one extra chromosome in one daughter cell, and one less chromosome in another Monosomy : the nucleus lacks one chromosome Trisomy : the nucleus has an extra chromosome o Most aberrancies that lead to miscarriages are trisomies o Trisomy 21/Down Syndrome : extra chromosome 21- Aberrancies are more common in older mothers, as they are using old oocytes that may have been damaged in the time since puberty- Sex chromosome aberrancies (most caused by nondisjunctions): o XO, Turners Syndrome (monosomy): Occurs when an egg lacking an X chromosome (resulting from a nondisjunction) is fertilized by a sperm bearing an X chromosome Women w/Turners have underdeveloped ovaries o XXY, Klinefelters Syndrome (trisomy): Occurs when nondisjunction retains two X chromosomes Women w/Klinefelters Syndrome have predominantly male features (small testes, etc.), and breasts in some cases o XXX, Super Females: Same cause as Klinefelters Syndrome...
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This note was uploaded on 05/01/2008 for the course BIO SCI 75 taught by Professor Sander during the Winter '07 term at UC Irvine.
- Winter '07