Final answer:
Ethyl methane sulfonate (EMS) is commonly used as a chemical mutagen for genetic screens because it induces point mutations by methylating guanine bases in DNA. The correct option is a.
Step-by-step explanation:
The chemical mutagen commonly used for genetic screens is Ethyl methane sulfonate (EMS). EMS is a powerful mutagen that works by methylating the guanine base in DNA, which leads to mistakes in base pairing during DNA replication and thus induces point mutations.
This chemical is known for being toxic and carcinogenic. The Ames test is a biological assay that uses bacteria to assess the mutagenic potential of chemical compounds like EMS.
Understanding the mechanisms of different mutagenic agents, such as ethyl methane sulfonate, helps in evaluating the potential carcinogenic risks associated with them. The correct option is a.