Hybrid vigour is due to

The $F_2$ dihybrid ratio $9 : 3 : 4$ is explained on the basis of

In a certain plant species,red flower colour is incompletely dominant to white flower colour (the heterozygote is pink) and tall stems are completely dominant to dwarf stems. If a tall pink plant $(TtRr)$ is crossed with a tall white plant $(TTrr)$,which one of the following types of plants would be produced in the offspring?

Define/Explain the following terms:
$1.$ Genotype
$2.$ Variation

What percentage of genes does a child receive from his father?

What is the practical utility of genetics?