Which of the following was $NOT$ included in Mendel's laws?

The phenomenon that acts against linkage is......

$A$ pure breeding pea plant with the dominant phenotype of character $A$ and recessive phenotype of character $B$ was crossed with another pure breeding plant with the recessive phenotype of $A$ and dominant phenotype of character $B$. An offspring of this cross was crossed with a homozygous recessive for both the characters $A$ and $B$. The following results were obtained:
$22$ were phenotypically dominant for $A$ and recessive for $B$.
$4$ were phenotypically dominant for both $A$ and $B$.
$4$ were phenotypically recessive for both $A$ and $B$.
$24$ were phenotypically recessive for $A$ and dominant for $B$.
These results show that:

When two genes are situated very close to each other on a chromosome:

Which event during cell division is responsible for the emergence of new characteristics in the next generation of organisms?

Why did Morgan choose the fruit fly for his experiments to prove the chromosomal theory of inheritance?