What is the cross between the progeny of $\mathrm{F}_{1}$ and the homozygous recessive parent called? How is it useful?

Test cross in plants or in Drosophila involves crossing

Mendel crossed a pure white-flowered recessive pea plant with a dominant pure red-flowered plant. The first generation of hybrids from the cross should show

Mendel’s law of sagregation is applicable to

$BB =$ for black colour alleles

$bb =$ for brown colour alleles

Offspring of a cross between a black mouse and brown mouse allowed to interbreed than find out the percentage of black coat in them