system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if each parent only has either XX or XY chromosomes, how can a child get a disorder like pentasomy X (having XXXXX chromosomes)?
gpt
Cell division is preceded by copying of all the chromosomes and splitting them between the two resulting cells. Nondisjunction can happen, which means the two copies don't split evenly and migrate to their corresponding new cells and they may all end up on one side and make a cell with double the normal amount. Repeat this a couple times and mess up the last one so only one X goes with the one that already has 4 and you end up with 5.