The parent's paternal and maternal chromosomes recombine to produce the corresponding chromosome in the egg or sperm:

Paternal: gtacgatcgtagatcgatcatatccgtacgcatcatgactacatatcatcgatcgatcatcatatcgatcatcagcatcgatcgatcgatcgatcgat
Maternal: gggggggggggggggaccagtatgtatcagtcctattactacatctactataactatctactagctagcaatatcctactcatacatctacttactgt

Combined: gtacgatcgtagatcgatcatatctatcagtcctattactacatctactataacgatcatcatatcgatcatcacctactcatacatctacttactgt

In practice, cross-overs are much less frequent than in this stylised example: on average, there are 798,852 total letters per cM or 190 letters observed per cM, or one recombination or crossover per generation per 19,000 observed letters.

Cross-over locations are different for every sperm produced by a man and for every egg produced by a woman.