Chapter 12.txt

  1. alleles
    One of two or more molecular forms of a gene at a given locus; alleles arise by mutation and encode slightly different versions of the same trait.
  2. aneuploidy
    A type of chromosome abnormality in which body (somatic) cells have one extra or one less chromosome relative to the parental chromosome number.
  3. autosomes
    Of a sexually reproducing species, any chromosome of a type that is the same in both males and females.
  4. crossing over
    At prophase I of meiosis, reciprocal exchange of segments between two nonsister chromatids of a pair of homologous chromosomes. Puts novel combinations of alleles in gametes.
  5. deletion
    Loss of a chromosome segment; often leads to genetic disorders. Also the loss of one or more nucleotide bases from a DNA molecule.
  6. duplication
    Base sequence in DNA that has been repeated two or more times.
  7. embryo
    Of animals, a new individual that forms by cleavage, gastrulation, and other early stages of development. Of plants, a young sporophyte until germination.
  8. fetus
    In mammalian development, the stage after all major organ systems have formed until time of birth.
  9. gene
    Unit of heritable information in DNA, transmissable from parents to offspring.
  10. genetic abnormality
    A less common or rare version of a heritable trait.
  11. genetic disorder
    An inherited condition causing mild to severe medical problems.
  12. genetic recombination
    Outcome of any process that puts new genetic information in a DNA molecule; e.g., by crossing over.
  13. inversion
    A chromosomal alteration; part of the DNA sequence gets oriented in the reverse direction, with no molecular loss.
  14. karyotype
    Preparation of an individual´┐Żs metaphase chromosomes arranged by length, centromere location, and shape.
  15. linkage groups
    All genes on a chromosome.
  16. nondisjunction
    Failure of sister chromatids or homologous chromosomes to move apart in meiosis or mitosis. Daughter cells get too many or too few chromosomes.
  17. pedigree
    Chart of connections among individuals related by descent.
  18. polyploidy
    A case of somatic cells having three or more of each type of chromosome characteristic of the species.
  19. reciprocal crosses
    A paired cross that may identify the role of parental sex on the inheritance of a trait. In the second cross, a trait characteristic of each sex is reversed compared to the original cross.
  20. sex chromosomes
    One of two kinds of homologous chromosomes that, in certain combinations, dictate the gender of the new individual. Also has genes unrelated to sexual traits.
  21. testosterone
    A sex hormone necessary for the development and functioning of the male reproductive system of vertebrates.
  22. translocation
    Attachment of a piece of a broken chromosome to another chromosome. Also, a mechanism by which organic compounds are conducted in phloem.
  23. trisomy 21
    Having one extra chromosome in somatic cells; e.g., trisomy 21 (2n + 1).
  24. wild-type allele
    Of a given gene locus, the allele that occurs normally or with the greatest frequency among individuals of a population.
  25. X chromosome
    A type of sex chromosome that influences sex determination; e.g., XX mammalian embryo becomes female; an XY pairing causes it to develop into a male.
  26. X-linked inheritance
    Recessive condition in which the responsible, mutated gene is on the X chromosome.
  27. Y chromosome
    Distinctive chromosome in males or females of many species (not both); e.g., human males XY, females, XX.
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Chapter 12.txt
Chapter 12