Chapter 10.txt

  1. allele
    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. asexual reproduction
    Any reproductive mode by which offspring arise from one parent and inherit that parent�s genes only; e.g., prokaryotic fission, transverse fission, budding, vegetative propagation.
  3. centromere
    Of a eukaryotic chromosome, a constricted region having binding sites (kinetochores) for spindle microtubules.
  4. chromosome number
    The sum of all of the chromosomes in cells of a given type.
  5. clones
    A genetically identical copy of DNA, a cell, or a multicelled organism.
  6. 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.
  7. diploid number
    Of many sexually reproducing species, having two chromosomes of each type, or pairs of homologues, in somatic cells.
  8. egg
    Mature female gamete, or ovum.
  9. fertilization
    Fusion of a sperm nucleus and an egg nucleus, the result being a single-celled zygote.
  10. gametes
    Haploid cell formed by meiotic cell division of a reproductive cell; required for sexual reproduction.
  11. gametophyte
    [Gk. phyton, plant] A haploid multicelled body in which haploid gametes form during the life cycle of plants and some algae.
  12. genes
    Unit of heritable information in DNA, transmissable from parents to offspring.
  13. genetic recombination
    Outcome of any process that puts new genetic information in a DNA molecule; e.g., by crossing over.
  14. germ cells
    Animal cell set aside for sexual reproduction; gives rise to gametes.
  15. haploid number
    The sum of all chromosomes in cells with one of each type of chromosome characteristic of the species; e.g., in a gamete.
  16. homologous chromosomes
    [Gk. homologia, correspondence] One of a pair of chromosomes in body cells of diploid organisms; except for a pairing of nonidentical sex chromosomes, a pair has the same size, shape, and gene sequence.
  17. meiosis
    [Gk. meioun, to diminish] A nuclear division process that halves the parental chromosome number, to a haploid (n) number. Prerequisite to the formation of gametes and sexual spores.
  18. oocyte
    A type of immature egg.
  19. ovum
    Mature secondary oocyte.
  20. polar body
    One of four cells that form by meiotic cell division of an oocyte but that does not become the ovum.
  21. sexual reproduction
    Production of genetically variable offspring by meiosis, gamete formation, and fertilization.
  22. sister chromatids
    One of the two attached members of a duplicated eukaryotic chromosome.
  23. sperm
    Mature male gamete.
  24. spores
    A structure of one or a few cells, often walled or coated, that protects and/or disperses a new sexual or asexual generation. Many bacteria as well as apicomplexans, fungi, and plants form spores.
  25. sporophytes
    [Gk. phyton, plant] A sporeproducing vegetative body of a plant or multicelled alga that grows by mitotic cell divisions from a zygote.
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Chapter 10.txt
Chapter 10