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 a test cross involving $F_1$ dihybrid flies, more parentaltype offspring were produced than the recombinanttype offspring. This indicates
Crossing over is
Alleles of different genes that are on the same chromosome may occasionally be separated by a phenomenon known as
$A$ : Morgan's cross III was conducted in Drosophila to locate genes on chromosome for white eye colour.
$R$ : The cross was done between red eyed hybrid female and white eyed male.
Assertion : In case of incomplete linkage, linked gene show new combination along with parental combination.
Reason : In case of incomplete linkage, linked genes are separated by crossing over.