When two genes are located on the same chromosome, what is the physical basis for the production of recombinant offspring in a testcross between a dihybrid parent and a double-mutant (recessive) parent?

The thread-like structure present in the cell nucleus with DNA wound in it is known as a chromosome. It is passed from the parent to the offspring. The genetic information is coded in it and passed to the offspring.

The recombinant offspring are the offspring that possess different allele combinations compared to the parents. The recombination process produces recombinant offspring. The main aim of creating recombinant offspring is to increase genetic diversity.

Meiosis is the type of cell division that takes place in the germ cells.Crossing over occurs in meiosis I. The similar DNA sequences present in chromosomes cross over each other, resulting in the formation of recombinants.

The crossing-over process takes place in the heterozygous parent resulting in recombinant genotypes. Double mutant parent produces the offspring with the recombinant gametes via the process of fertilization.

Hence, the crossing over is the mechanism that produces recombinant offspring.