GEN BIO

• Chromosome


  A continuous molecule of DNA with associated proteins; in humans, a diploid cell contains 22 homologous pairs of autosomes and one pair of sex chromosomes
• 1. linked recessive disorders


  Affect more males than females; a male expresses every allele on his one X chromosome, while a female has two X chromosomes and may inherit a dominant allele that masks the expression of a recessive one
• Polymerase chain reaction (PCR)


  Replicates DNA in a test tube by separating DNA into two strands and having DNA polymerase add complementary nucleotides to each strand, with repeated cycles of heating and cooling allowing for rapid amplification of the target DNA sequence
• Genetic testing


  Uses DNA probes to detect disease-causing alleles in cells from a fetus, child, or adult
• Alternation of generations


  The plant life cycle includes a diploid sporophyte generation that undergoes meiosis to produce haploid spores, which give rise to the haploid gametophyte generation that produces gametes
• Seed germination


  Requires oxygen, water, and favorable temperature to resume the embryo's development
• Gibberellins


  Plant hormones that stimulate cell division and elongation, and help break seed dormancy
• Auxins


  • Stimulate cell elongation in shoot tips, embryos, young leaves, flowers, fruits, and pollen
  • Most concentrated at the main shoot tip, which blocks the growth of lateral buds (apical dominance)
• Abscisic acid


  • Counters the growth-inducing effects of other hormones by inducing dormancy and inhibiting shoot growth
• Epithelial tissue


  • Lines and covers organs, forms glands
  • Protects the underlying tissue, senses stimuli, and secretes substances
  • May be simple (one layer) or stratified (more than one layer), and the cells may be flat, cube-shaped, or columnar
• Neurons


  • Consist of a cell body, dendrites, and an axon
  • Fatty neuroglia wrap around portions of some axons to form the myelin sheath