What will be the number of linkage groups in maize if it has $10$ pairs of chromosomes?

For the preparation of genetic maps,the recombination frequencies between genes are additive over short distances but not over long distances due to

Incomplete linkage is $A$. Complete linkage is $B$. Choose the correct option for $A$ and $B$.

Two genes '$a$' and '$b$' show $20\%$ recombination. What will be the proportion of gametes produced by a dihybrid $F_1$ individual with the genotype $++/ab$,derived from a cross between $++/++$ and $ab/ab$?

Linkage was first observed in

Linkage was first studied by .....