Chapter 15.txt

  1. ABC model
    Model for the genetic basis of flower formation; products of three master genes (A, B, C) control the development of sepals, petals, and stamens and carpels from meristematic tissue.
  2. acetylation
    The attachment of an acetyl group (CH3CO) to an organic compound.
  3. Barr body
    Of the two X chromosomes in the somatic cells of female mammals, the one that has been condensed.
  4. cell differentiation
    In developing embryos of multicelled organisms, the process by which different cell lineages selectively express a different fraction of their genome and thereby become specialized in their composition, structure, and function.
  5. dosage compensation
    A gene control mechanism in female mammals in which most genes on one of two X chromosomes in somatic cells are inactivated; ensures that X chromosome genes are expressed at the same levels as in males (XY).
  6. enhancers
    A small sequence in DNA that binds transcription-regulating molecules; enhances transcription rates.
  7. gene controls
    A molecular mechanism that governs if, when, or how a specific gene is transcribed or translated.
  8. homeotic genes
    One of a class of master genes; helps determine identity of body parts during embryonic development.
  9. hormones
    [Gk. hormon, stir up] Signaling molecule secreted by one cell that can alter activities of any cell with receptors for it.
  10. introns
    One of the noncoding sequences in eukaryotic genes; it is excised from the pre-mRNA transcripts before translation.
  11. knockout experiments
    An experiment in which a living organism is engineered so that one of its genes does not function.
  12. methylation
    Attachment of a methyl group to an organic compound; also a common gene control mechanism.
  13. mosaic tissue effect
    In female mammals, an outcome of random X chromosome inactivation; different patches of tissue are expressing different X-linked alleles.
  14. negative control
    Control mechanism by which one or more regulatory proteins slow down a cell activity.
  15. operator
    Part of an operon; a DNA binding site for a regulatory protein.
  16. operon
    Group of bacterial genes together with a promoter´┐Żoperator DNA sequence that controls their transcription.
  17. pattern formation
    In animal embryonic development, the sculpting of specialized tissues and organs from clumps of cells in the proper places, in the proper order by way of embryonic induction.
  18. polytene chromosomes
    Of some insects, a chromosome consisting of many parallel copies of the same DNA molecule.
  19. positive control
    Use of regulatory proteins to promote gene expression.
  20. promoter
    Short stretch of DNA to which RNA polymerase binds. Transcription then begins at the gene closest to the promoter.
  21. promoters
    Short stretch of DNA to which RNA polymerase binds. Transcription then begins at the gene closest to the promoter.
  22. regulatory proteins
    Part of mechanisms that control transcription, translation, and gene products by interacting with DNA, RNA, new polypeptide chains, or proteins such as enzymes.
  23. repressor
    Type of protein that can block transcription of a prokaryotic gene by binding to an operator.
  24. selective gene expression
    Outcome of controls over which gene products a cell makes or activates in a specified interval. Basis of cell differentiation.
  25. X chromosome inactivation
    In a female mammalian embryo, the programmed painting of special RNAs over most of one of the two X chromosomes, which cuts off access to the majority of its genes. Which X chromosome gets painted in each cell is a random event, so tissues of adult female mammals are a mosaic of traits. See also Dosage compensation.
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Chapter 15.txt
Chapter 15