Lab 10 summary CC-BY-NC

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Summary of Lab 10 for BIOL 112 (Winter 2011). Week of Mar 14 2011.


Genetics: recombination and mapping problems.


  • Probability-wise, you encounter ~20 amino acids before encountering a stop codon (just by chance)
  • Open reading frame: does not contain stop codons
    • Three reading frames for each stretch of DNA for obvious reasons
    • Although you could potentially have a sequence coding for three overlapping proteins (one in each ORF) it's unlikely
    • If you find an ORF that codes for more than 60 amino acids then it's probably coding for a protein
  • Although DNA is not random, it will appear random if you try to translate it unless it codes for a protein in that reading frame
  • All genes start with the methionine codon (ATG), end with a stop codon (TAG etc)
  • We can use the SeqBuilder program to see if a given protein is similar to other proteins etc
    • And even make a phylogenetic tree omg!!
  • Organisms have more than one DNA polymerase because there is more than one mRNA to be formed in the cell at any given time


  • Happens during prophase I of meiosis
  • When genes on the same chromosome, they are considered linked
    • However, when two chromosomes (homologs) exchange material, recombination occurs
    • Cis-arrangement: a+b+/ab
    • Trans-arrangement: a+b/ab+
    • Recombination rate depends on distance between genes - genes located close together will be recombined less often
    • Recombined 1% of time --> 1 map unit away, etc
    • Loci - place occupied by genes on chromosomes; correspond to map units
  • In Drosophila, genetic recombination occurs only in the female on autosomes and allosomes (does not occur in males)
  • For genetic recombination problems:
    • The least common progeny are the result of recombination
    • Use that to figure out what the original arrangement was (cis or trans)
    • You can calculate distance (in map units) from percentages etc