The frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes was explained by

The four daughter cells derived from a single meiosis differ from each other due to

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

Genetic map is one that

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:

$A$ : Crossing over is exchange of genetic material between non-homologous chromosomes.
$R$ : It produces new linkages.