What is the genotype for the tall plant?
Is it TT or Tt?
If a farmer only wants to grow tall plants to sell, how does she ensure that there are no small plants?
She only breeds the plants with the TT genotype.
How does she know which plant has the TT genoptype?
Carry out a test (back) cross.
Test (back) cross
The genotypes TT and Tt both produce a tall phenotype. In order to establish the genotype, a test cross is used.
The organism in question is crossed with a homozygous recessive individual (tt).
If no short plants (tt) are produced in the offspring the unknown parent was homozygous (TT).
If any short plants (tt) are present in the offspring the unknown parent was heterozygous (Tt).