How many linkage groups are present in bacteria?

Discuss why Drosophila has been used extensively for genetical studies.

Which of the following statements are correct?

$A$ 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.

The first mutant gene reported by $T.H. Morgan$ in $Drosophila$ was the . . . . . . .

The number of linkage groups in a cell having $10$ pairs of chromosomes is.....