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, crossovers 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.

Crossover locations are different for every sperm produced by a man and for every egg produced by a woman.