Lab 9 summary CC-BY-NC

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Summary of Lab 9 for BIOL 112 (Winter 2011). Week of Mar 7 2011.

Human genetics: salivary chromosomes.

Genetics problems: test cross - sex-linked traits.

1Human genetics

  • In human genetics, upper case = dominant, lower = recessive
  • But we're mavericks and will continue the use the nomenclature from previous labs
  • Ability to taste PTC: non-sex-linked; tasters are dominant (70% of population)
  • Sex-linked traits:
    • On the X- or Y-chromosome only
    • Colourblindness for example
  • Test-cross: find out the genotype of a wild-type organism by mating it to a mutant-type (homozygous recessive)
  • For genetics problems, just diagram it, it's not that hard

2Salivary chromosomes

  • Salivary glands of certain insect larvae have chromosomes hundreds of times larger than normal
  • Called polytene chromosomes; result of repeated replication without separation of chromosomes
  • Chromosomes have banded appearance - chromatin fibres are alternatingly extended and coiled
  • Puffs - swollen bands, genetic sites active in mRNA synthesis ?
  • Chromocentre: all four pairs of chromosomes attached by centromeres
  • Take a Drosophila larva, decapitate it, get the salivary glands D: