Bio exam 3

• Meiosis


  A process that reduces the number of chromosome sets from diploid to haploid, producing genetically distinct cells
• Sexual reproduction


  Two parents give rise to offspring that have unique combinations of genes inherited from the two parents
• Asexual reproduction


  A single individual passes all its genes to its offspring without the fusion of gametes
• Clone


  A group of genetically identical individuals from the same parent
• Meiosis is more efficient at producing genetic variation among offspring compared to asexual reproduction
• Life cycle


  The generation-to-generation sequence of stages in the reproductive history of an organism
• Homologous chromosomes


  Chromosomes in a pair that are the same length and shape and carry genes controlling the same inherited characters
• Diploid cell


  A cell with two sets of chromosomes
• Haploid cell


  A cell with a single set of chromosomes
• Meiosis


  1. Prophase I

  2. Metaphase I

  3. Anaphase I

  4. Telophase I and Cytokinesis

  5. Prophase II

  6. Metaphase II

  7. Anaphase II

  8. Telophase II and Cytokinesis
• Meiosis


  • Reduces the number of chromosome sets from diploid to haploid
  • Produces genetically distinct cells
• Mitosis


  • Conserves the number of chromosome sets
  • Produces genetically identical cells
• Three events unique to meiosis are synapsis and crossing over in prophase I, homologous pairs at the metaphase plate, and separation of homologs during anaphase I
• Mutations are the original source of genetic diversity
• Alleles


  Different versions of genes
• Mechanisms contributing to genetic variation

  1. Crossing over

  2. Independent assortment of chromosomes

  3. Random fertilization
• The number of possible chromosome combinations from independent assortment is 2^n, where n is the haploid number
• Random fertilization adds to genetic variation because any sperm can fuse with any ovum
• Independent assortment is accomplished by the random orientation of homologous pairs of chromosomes at metaphase I of meiosis
• Gene expression


  The process by which DNA directs protein synthesis, includes two stages: transcription and translation
• Genes


  • The information content of genes is in the specific sequences of nucleotides
  • DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins
  • Proteins are the links between genotype and phenotype
• Gene expression


  1. Transcription

  2. Translation
• Transcription


  The synthesis of RNA using information in DNA
• Translation


  The synthesis of a polypeptide, using information in the mRNA
• Ribosomes


  The sites of translation
• Beadle and Tatum exposed bread mold to X-rays, creating mutants that were unable to survive on minimal media
• Identifying nutritional mutants in Neurospora

  1. Cells placed on complete medium

  2. Cells subjected to X-rays

  3. Surviving cells form colonies

  4. Cells placed in minimal medium

  5. Nutritional mutants identified

  6. Nutritional mutants placed in vials with a variety of media

  7. Observe for growth
• Class I mutants


  Mutation in gene A, can grow only on citrulline or arginine
• Class II mutants


  Mutation in gene B, can grow with or without any supplements
• Class III mutants


  Mutation in gene C, can grow on ornithine, citrulline, or arginine
• RNA is the bridge between genes and the proteins for which they code
• In prokaryotes, translation of mRNA can begin before transcription has finished
• In a eukaryotic cell, the nuclear envelope separates transcription from translation
• Eukaryotic RNA transcripts are modified through RNA processing to yield the finished mRNA
• Primary transcript


  The initial RNA transcript from any gene prior to processing
• Central dogma


  Cells are governed by a cellular chain of command: DNA → RNA → protein
• Triplet code


  A series of nonoverlapping, three-nucleotide words that are transcribed and translated
• The genetic code is redundant (more than one codon may specify a particular amino acid) but not ambiguous (no codon specifies more than one amino acid)
• Codons must be read in the correct reading frame (correct groupings) for the specified polypeptide to be produced
• Transcription


  The first stage of gene expression, catalyzed by RNA polymerase