Answer:
25%
Explanation:
We have 2 independent genes with 2 alleles each: L/l and W/w
Individuals with short whiskers will have the genotype WWll or Wwll.
A cross between a rat heterozygous for both genes and a homozygous recessive rat is done:
-The homozygous rat will produce only wl gametes.
-The heterozygous rat will produce the following gametes: WL, Wl, wL, wl.
If you do a Punnett Square, you'll get that 25% of the offspring will be WwLl and will have short whiskers.