164 MCB S09 April 27 2009 In class exercise #3 Score: Key
Names of group members
1. You have created a mouse model for shrunken toenail syndrome and find that two genes act in a simple enzymatic pathway to create smooth toenails, BLUETOE (BT) and SHRUNKEN TOENAIL (ST). A bt-/- null mutant has smooth blue toenails and a st-/- null has white shrunken toenails.
ST A B
BT C
You cross 2 mice heterozygous for both genes. Po bt -/+; st -/+ X bt -/+ ; st -/+
Indicate what fraction of F1 progeny will exhibit the phenotypes listed below. Assume that null alleles are to recessive wild type and that st -/- is fully epistatic to bt -/- (i.e. bt -/- ; st -/- animals have white shrunken toenails).
Smooth white: bt +_; st +/_ (3/4) x (3/4) = 9/16 Smooth blue: bt -/-; st +_ (1/4) (3/4) = 3/16 Shrunken white: bt any; st -/- (1/4) = 4/16 Shrunken blue: 0
2. You find a dominant gain-of-function allele of BT that gives purple toenails (btD). Based on the pathway shown above, predict the phenotype of a bt D/+ ; st -/a) b) c) d) e) f) shrunken white shrunken purple shrunken blue nonshrunken white nonshrunken purple nonshrunken blue