Question

When does a genetic need to carry test cross and its caarried out ?

Answer 1

Test crosses are used to test an individual's genotype by crossing it with an individual of a known genotype. Individuals that show the recessive phenotype are known to have a homozygous recessive genotype. Individuals that show the dominant phenotype, however, may either be homozygous dominant or heterozygous

Answer 2

The crossing of an organism, with an unkown genotype, to a homozygous recessive organism (tester). A cross between an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a homozygous recessive individual.  

Test cross can be used to decide the genotype of the F1 generation. The test cross can be used to support the idea that the recurrence of the recessive character in the F2 generation is due to the heterozygous condition of the F1 . The test used to prove whether any given pair of traits could be alleles (different characters).