Which of the following crosses will result in 100% heterozygous offspring? 
Cross I          P:  TT × tt 
Cross II         P:  Gg × Gg 
Cross III        P:  RR × RR 
Cross IV        P:  YY × yy 

• A. Cross II only
• B. Cross III only
• C. Cross I and IV
• D. Cross 1 and III

Answer: (C)