Give scientific reasons : Linkage and crossing over of genes are alternatives of each other.
The gene for haemophilia is present on $X$-chromosome. $A$ male has only one $X$-chromosome which he receives from his mother and $Y$-chromosome from father. The human male passes the $\mathrm{X}$ chromosome to his daughters but not to the male progeny (son).
In Drosophila, long wing and broad abdomen characters are dominant over to characters vestigeal wing and narrow abdomen. A pure breeding Drosophila having long wings and broad abdomen is crossed with a pure breeding vestigeal-winged and narrow-abdomened Drosophila. Two of the $F_1$ individuals were crossed and the following results were produced in the $F_2$ generation Long wing, broad abdomen in $482$ Drosophila. Vestigeal wing, narrow abdomen in $154$ Drosophila. Which one of the following is illustrated by these results
Morgan hybridised yellow-bodied, white-eyed females to brown-bodied, red-eyed males and intercrossed their $F_{1}$ progeny. He observed that
$(a)$ $F_{2}$ ratio was deviated very significantly from the $9 : 3 : 3 : 1$ ratio
$(b)$ Both genes did not segregate independently of each other
$(c)$ Recombinant types are not obtained in $F_{2}$ generation
$(d)$ Both genes segregate independently of each other
Select the correct set of statements :
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:
If gene exchange rate is $30\%$ of the two linked genes, then the distance between these two genes is