Lec7_illustrations

Lec7_illustrations - LECTURE 7 Tuesday, January 31...

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Announcements/reminders Dosage compensation/X-inactivation Changes in chromosome number Non-disjunction and aneuploidy Polyploidy Changes in chromosome structure Deletion, duplication, inversion, and translocation Behavior of chromosome variants during meiosis More about the midterm LECTURE 7 Tuesday, January 31 Chromosomes: Variation in number and arrangement
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Announcements/Reminders Get your ?s answered on the discussion board Get your ?s answered in section Get your ?s answered at office hours Imprinting supplement on ted.ucsd.edu Section questions/answers on ted.ucsd.edu Clicker questions/answers coming to ted.ucsd.edu
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Humans “inactivate” one X chromosome • Silence one female X chromosome so males and females express the same amount • X-inactivation: causes “Barr body”
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X inactivation follows N-1 rule • N is # of X chromosomes – # of Barr bodies is N-1
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Lyon hypothesis • Mary Lyon discovered X inactivation in 1961 • Random inactivation of either the maternal or paternal chromosome • Occurs early in embryonic development, and all cellular descendants have the same inactivated chromosome
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X-inactivation is maintained through several cell divisions • Creates “clones” or groups of cells that have one chromosome inactivated maternal paternal
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Female mammals are mosaics of X chromosome expression: some cells express maternal X some cells express paternal X
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XXY (Klinefelter syndrome) and XO (Turner syndrome) • Last time, we discussed these unusual chromosomal arrangements – How do these arrangements occur?
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Terminology for variation in chromosome number
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Mitosis vs. Meiosis
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Mechanics of chromosome separation during meiosis • A tetrad is a physical structure – 2 sister chromatids for each of 2 chromosomes • A dyad is a physical structure – 2 sister chromatids
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two different times in meiosis
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Lec7_illustrations - LECTURE 7 Tuesday, January 31...

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