In the construction of chromosome maps,the evidence is derived mainly from

The frequency of recombination will be higher if.....

The phenomenon that acts against linkage is......

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:

Gene-mapping technology was developed by

Sex linkage was first observed by.....