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.
- 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
- 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: