(a) B - C - D - E - F - G - H - I - J - K (or) A- B - C - D - E - F - G - H - I - J.
(b) A- B - C - D - E - F - E - F - G - H - I - J - K.
(c) A - B - E - D - C - F - G - H - I - J - K.

After tetrad formation, crossing over occurs in pachytene stage. The non-sister chromatids of homologous pair make a contact at one or more points. These points of contact between non-sister chromatids of homologous chromosomes are called Chiasmata (singular-Chiasma). At chiasma, cross-shaped or X-shaped structures are formed, where breaking and rejoining of two chromatids occur. This results in reciprocal exchange of equal and corresponding segments between them.

The two dominant alleles or recessive alleles occur in the same homologous chromosomes, tend to inherit together into same gamete are called coupling or cis configuration. If dominant or recessive alleles are present on two different, but homologous chromosomes they inherit apart into different gamete are called repulsion or trans configuration.

Crossing over results in the formation of new combination of characters in an organism called recombinants. In this, segments of DNA are broken and recombined to produce new combinations of alleles. This process is called recombination.
The widely accepted model of DNA recombination during crossing over is Holliday's hybrid DNA model.