Question

Work out a cross to find the genotype of a tall pea plant. Name the type of cross.

Answer 1

A test cross is carried out to find out whether an organism having a dominant phenotype is homozygous or heterozygous for the trait. In a test cross, the cross is carried out between a homozygous recessive organism and another organism showing the dominant phenotype. If the organism showing the dominant phenotype has homozygous alleles than the resulting F1 generation will have organisms all of which show the dominant character and their genotype will be heterozygous for the trait. If however, the organism has a heterozygous genotype for the dominant trait then the resulting F1 generation will have half of the organisms of the dominant phenotype and half of the recessive phenotype. This cross can be shown by a cross for the tall (dominant) or dwarf (recessive) feature of pea plant as shown. Thus, if the result is all tall plants then the genotype of the parent will be homozygous dominant (TT) and if the result is 50% tall and 50% dwarf then the parent will be heterozygous dominant (Tt).