What is the mechanism of moving a segment from one linkage group to another called?

The rate of appearance of new forms is linked to which of the following?

The defect sickle-cell anaemia is caused by the . . . . . . of glutamic acid by valine at the $6^{th}$ position of the . . . . . . globin chain of the haemoglobin molecule.

Mutation is an error that occurs during cell division.

Duplication of one or two bases of $DNA$ produces . . . . . . .

Which phenomenon leads to the variation in $DNA$?