Definitions / Explanation : Test cross
 

When a true breeding pea plant that has yellow seeds is pollinated by a plant that has green seeds, all the $F_1$ plants have yellow seeds. This means that the allele for yellow is

Variation stands for differences in traits of progenies from

$A$ : Test cross is the tool for knowing linkage between genes.
$R$ : Monohybrid test cross gives two phenotypes and two genotypes.

Self pollination between $Tt$ and $Tt$ plants results into genotype ratio of