determine the genotype of a plant at $\mathrm{F}_2$
predict whether two traits are linked
assess the number of alleles of a gene
determine whether two species or varieties will breed successfully
Solution
When $\mathrm{F}_1$ hybrid is crossed with its recessive parent, it is called test cross. By test cross heterozygosity and homozygosity of the organism can be tested. It gives $1: 1$ ratio in monohybrid and $1: 1: 1: 1$ ratio in dihybrid condition. In presence of linkage the ratio varies from this.