BIO105 FINALS

• Every cell nucleus contains the complete genome established in the fertilized egg. In molecular terms, the DNAs of all differentiated cells are identical.
• The unused genes in differentiated cells are not destroyed or mutated, and they retain the potential for being expressed.

  
• Only a small percentage of the genome is expressed in each cell, and a portion of the RNA synthesized in the cell is specific for that cell type.
• Differentiation


  The process by which an individual cell acquires a specialized function
• Differentiation requires a change in the pattern of gene expression in a cell.
• Differential Gene Expression


  Different sets of genes are active (turned ON) in different types of cells
• Gene Amplification


  Selective increase in the number of copies of a gene coding for a specific protein without a proportional increase in other genes

  
• Giant Chromosomes


  • Polytene chromosomes in the salivary gland cells of the fruitfly Drosophila (~2000 μm in length)
  • Lampbrush chromosomes in the oocytes of amphibians and some insects (~1500 to 2000 μm in length)
• Polytene Chromosomes


  • Formed by the fusion of centromeres of all the 8 chromosomes found in the cell
  • Parts: arms (long and short) and chromocenter
  • Show characteristic dark bands (chromomeres) and light bands (chromonemata)

  
• Polytene chromosomes in Drosophila are produced by endoreplication (in cells of the larval salivary glands of many Dipteran species) to increase production of mRNA for Glue Protein
• In certain cell types, particular regions of the chromosomes would occasionally form different reversible puffs (chromosome puffs or Balbiani rings) which are associated with differential gene activation.
• Lampbrush Chromosomes


  • Consist of an axis with chromomeres and interchromomere regions, and loops which consist of transcriptionally active DNA

  
• Reticulocytes synthesize hemoglobin.
• Morphogenesis


  The process by which differentiated cells are organized into a hierarchy of tissues, organs, and organ systems
• Molecular Traffic through Nuclear Pore Complexes

  • Model of the nuclear pore complex
  • Transport of Proteins
  • Transport of snRNAs from nucleus to cytoplasm
  • Control of Macromolecular Synthesis in the Nucleus by the Cytoplasm
• Gene Effects on Embryonic Induction

  Induction experiment done on frog gastrula
• Mutations in key hormone-synthesis genes cause endocrine disorders
• Studies in mice have shown that interfering with the HOX15 gene can cause parathyroid gland aplasia.
• Hox Family of Genes


  Important in controlling the anatomical identity of different parts of a body along its anterior/posterior axis
• In humans, the homeobox gene family contains an estimated 235 functional genes and 65 pseudogenes. These genes are present on every human chromosome, and they often appear in clusters.
• Homeobox Genes


  A large family of similar genes that direct the formation of many body structures during early embryonic development
• Effects of Genes on Migrating Cells

  Cell migration is fundamental to the morphogenesis of embryos
• Effects of Genes on Regulation of Growth and Development

  Development of the Lungs