system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does having a baby with a sibling create deformities and weaker genes in said baby?
gpt
It doesn't unless the aforementioned siblings have recessive defects. You need to have two copies of recessive defects to see an effect. Two siblings are more likely to share a recessive defect since they share a parent that could have one. If both siblings have this defect and pass it on, then the offspring will definitely exhibit the mutation.