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 $B. A$ offspring of this cross was crossed with a homozygous recessive for both the characters -$A$ and $B$. The following results are 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

The salivary gland chromosomes in the dipteran larvae, are useful in gene mapping because

In tryptophan operon

Tizo and Levan's contribution is very significant because they

Segments of $mRNA$ removed during splicing are called……