Genetic maps of chromosomes are based on the frequency of $:-$

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 $ab/ab$?

$A$ scientist performed a gene mapping experiment in maize. He mapped genes on chromosomes based on the percentage of crossing over between different genes. One map unit corresponds to $1\%$ crossing over or recombination frequency. Based on the study of crossing over in maize, the scientist observed the following recombination percentages between genes $A, B, C,$ and $D$: $A$ and $D = 10\%$, $A$ and $C = 3\%$, $C$ and $D = 7\%$, $A$ and $B = 5\%$, and $C$ and $B = 8\%$. Based on these observations, determine the correct order of genes $A, B, C,$ and $D$ on the chromosome.

Discuss in detail the contributions of Morgan and Sturtevant in the area of genetics.

The presence of recombinants is due to.....

Linkage was first studied by .....