Question

What is a test cross? How can it decipher the heterozygosity of a plant?

Answer 1

Gregor Mendel conducted hybridization experiments on garden peas for 7 years and proposed a law of inheritance by crossing different generations of garden pea plants. Mendel conducted such artificial pollination or cross pollination experiments using several true breeding pea lines.

Complete answer:
1. Mendel conducted a monohybrid cross in which inheritance of one gene was taken. And also conducted a hybrid cross in which inheritance of Two genes were taken. Experimenting on Mendel he saw some plants that were phenotype dominant with mixed genotypes. Which has both the genes of dominance and recessive.

2. From the Mendel experiment the phenotype could be known by seeing the plant. But the genotype of a plant cannot be that easily determined.

3. Since by looking at the phenotype of a dominant trait it is not possible to know the genotype composition. For example whether a tall plant has TT ( that means dominant and dominant ) or Tt ( which means dominant and recessive ) composition cannot be predicted.

4. To determine the genotype of a tall plant at F2 generation, Mendel crosses the tall plant from F2 the dwarf plant. This was called by Mendel as a test cross.

5. In a typical test cross an organism in Mendel case it was the pea plant showing a dominant phenotype and whose genotypes to be determined is crossed with the recessive parent instead of self crossing.

6. The progeny of such a cross can easily be analysed to predict the genotype of the test organism.

Note: Based on the observation Mendel proposed three laws of genetics, law of segregation law of dominance and law of independent assortment.