Which of the following statements is not true with respect to variation?

When Mendel crossed a tall plant with a dwarf plant,what was the ratio of dwarf plants in the $F_{2}$ generation (in $, \%$)?

Why are males considered heterogametic?

$A$ pea plant with blue colour flower denoted by $BB$ is cross-bred with a pea plant with white flower denoted by $ww$.
$(a)$ What is the expected colour of the flowers in their $F_{1}$ progeny?
$(b)$ What will be the percentage of plants bearing white flower in $F_{2}$ generation,when the flowers of $F_{1}$ plants were selfed?
$(c)$ State the expected ratio of the genotypes $BB$ and $Bw$ in the $F_{2}$ progeny.

$(a)$ Why do we say that homozygous plants produce pure progeny?
$(b)$ Define heterozygous.
$(c)$ Explain how the process of speciation takes place.

Explain Mendel's concept of heredity, by giving three points.