The recombination frequency between the genes $a$ and $c$ is $5\%$,$b$ and $c$ is $15\%$,$b$ and $d$ is $9\%$,$a$ and $b$ is $20\%$,$c$ and $d$ is $24\%$,and $a$ and $d$ is $29\%$. What will be the sequence of these genes on a linear chromosome?

Mendel observed that some characters did not assort independently. Later researchers found it to be due to

Morgan hybridized yellow-bodied,white-eyed females to brown-bodied,red-eyed males and intercrossed their $F_{1}$ progeny. He observed that:
$(a)$ $F_{2}$ ratio deviated 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:

Which of the following is true about linkage?
$I.$ It is a phenomenon in which more recombinants are produced in $F_{2}$-generation.
$II.$ More parental combinations are produced in $F_{2}$-generation.
$III.$ Genotypes which are present in $F_{1}$ hybrid reappear in high frequency in $F_{2}$-generation.
$IV.$ It is a phenomenon in which two chromosomes are linked.

Generation of non-parental gene combinations is termed as

Linkage in Drosophila was first discovered by