question_answer 4)

Define and design a test-cross. 

Answer:

Crossing of F1 individual having dominant phenotype with its homozygous recessive parent is called test cross. The test cross is used to determine whether the individuals exhibiting dominant character are homozygous or heterozygous.                 Example: When a tall plant (TT) is crossed with dwarf plant (tt) in the F1 generation only tall plant (Tt) appear which is then crossed with homozygous recessive (tt) in a test cross. In the given diagram a test cross between tall heterozygous F1 hybrid with dwarf homozygous recessive parent (P1) produces tall and dwarf in equal proportion indicating that F1 hybrids are heterozygous.