Which of the following characteristics does not occur in pairs?

If two alleles for a particular trait in an organism are identical,it is called . . . . . .

Provide definitions/explanations for the following terms:
$1.$ Genetics
$2.$ Heredity

$A$ heterozygous purple flower is crossed with a recessive white flower. What is the ratio of the progeny?

What is the primary purpose of a test cross?

In a monohybrid cross of plants with red and white flowered plants,Mendel got only red flowered plants. On self-pollinating these $F_1$ plants,he got both red and white flowered plants in a $3:1$ ratio. Explain the basis of using $RR$ and $rr$ symbols to represent the genotype of plants of the parental generation.