Answer: insertion
Crossing over is when homologous* chromosomes exchange genes, resulting in gene combinations.
Deletion is when a base pair is deleted from DNA. Insertion is when a base pair is added to DNA. Both insertion and deletion are serious because every amino acid beginning at the mutation will most likely be incorrect. This will lead to a nonfunctional protein.
Base-pair substitution is a substitution of one base pair for another in DNA. The effects of this may be a silent** point, missense*** point, or nonsense**** point.
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*A pair of matching chromosomes. They have the same genes but can have different versions.
**A special case where no amino acids are affected.
***Affects one animo acid. The whole protein structure and function may or may not be disrupted.
****Results in a stop codon that shortens the protein.