Recombination is the exchange of DNA segments between the two copies of a chromosome (maternally inherited and paternally inherited). This occurs during the creation of an egg or sperm for the next generation. Each chromosome is cut at the same location, usually at one or two random spots (crossover points), and DNA segments are swapped between the two copies.
The newly formed chromosome in the egg will be a patchwork of contributions from the maternal grandparents, and the newly formed chromosome in the sperm will be a patchwork of contributions from the paternal grandparents, but there is still one copy of every gene. Some eggs and sperm will retain a complete copy of one grandparent's chromosome without recombination. The creation of each egg and sperm is an independent event, so siblings will inherit different portions of their grandparents' DNA.
- Autosomal testing: recombination by Steve Handy. DNA Genealogical Experiences and Tutorials blog, 3 November 2012.