Coupling and repulsion are the two faces of

In $Lathyrus$ $odoratus$,a hybrid blue-flowered and long-pollen plant is test-crossed with a homozygous recessive red-flowered and round-pollen plant. How many parental types are obtained when genes are present in the $cis$ stage in parents (in $\%$)?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$:
Mendel's law of independent assortment does not hold good for the genes that are located closely on the same chromosome.
Reason $(R)$:
Closely located genes assort independently.
In the light of the above statements,choose the correct answer from the options given below:

In the fruit fly $Drosophila$,the lack of independent assortment between genes $A$ and $B$ is due to .....

The experiment shown in the given figure has been carried out by Morgan to show the phenomenon of linkage and recombination. If in cross $I$,genes are tightly linked and in cross $II$,genes are loosely linked,then what will be the percentage of recombinants produced in cross $I$ and cross $II$ respectively?

The distance between two genes in a chromosome is measured in cross-over units,which represent: