In a typical test cross, a plant showing a dominant phenotype is crossed with a plant showing__________ phenotype.

Key Points

• Test cross -
  • It is a genetic cross of an organism with a dominant phenotype with an organism having recessive phenotype.
  • It is performed in order to determine the unknown genotype of an organism.
  • It helps us to know whether the dominant phenotype has a homozygous or heterozygous genotype.
• Homozygous - It is the condition in which the pair of alleles determining a phenotype is identical, either both dominant or both recessive.
• Heterozygous - It is the condition where 2 different types of alleles are present, one dominant and one recessive.
• Genotype - It is the allelic constitution of a gene determining a particular character.
• Phenotype - It is the expressed character.

• Mendel had chosen 7 traits for his experiments on garden pea, from which he observed these genetic crosses.
• Each of these traits had 2 distinct phenotypic characters - one dominant and one recessive.

Explanation:

• For example, let us take the trait of stem height with the phenotypes of tall and dwarf plants.
• The tall plants can be homozygous (TT) or heterozygous (Tt), while the dwarf plants are always homozygous recessive (tt).
• To determine the genotype of a tall plant, we would perform a test cross with a dwarf plant.
• The test cross may have 2 outcomes:
  • Case 1 - If the unknown tall plant is homozygous (TT), it would produce all tall plants (Tt).
  • Case 2 - If the unknown tall plant is heterozygous (Tt), would produce tall : dwarf plants in 1:1 ratio.

Additional Information

• Back cross -
  • It is the genetic cross between F1 generation and either of the parent.
  • It is performed to obtain an offspring with more phenotypic similarity with its parents.
  • It is mostly used for horticultural purposes and animal breeding.