Lab 9 summary

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: