Explain what a mutation is, how mutations change proteins and can be harmful, neutral, or beneficial, and describe examples of biotechnology such as selective breeding and genetic engineering (MA STE HS-LS3-2, HS-LS3-3 supporting).

What this topic is asking

The Massachusetts STE framework expects you to understand that mutations are the ultimate source of new genetic variation (HS-LS3-2), and to be able to discuss how humans use genetic knowledge in biotechnology. On the High School Biology MCAS, mutation questions usually connect back to protein synthesis (how a base change reaches the protein), while biotechnology questions ask you to describe a technique and weigh a benefit against a concern. The crosscutting concept is cause and effect, and the science practice is often obtaining, evaluating, and communicating information.

What a mutation is

Because DNA codes for proteins, a change in the DNA can change a protein. Recall the gene-to-protein pathway from protein synthesis and gene expression: a base change can change a codon, which can change an amino acid, which can change the protein's folded shape and so its function. This is the cause-and-effect chain the MCAS asks you to trace.

Harmful, neutral, or beneficial

Not all mutations matter, and not all are bad. A mutation can be:

• Harmful. The changed amino acid disrupts the protein's shape so it no longer works, which can cause a genetic disorder.
• Neutral. The mutation has no effect on the protein. This often happens because the genetic code is redundant (more than one codon codes for the same amino acid), so the same amino acid is still placed; or the mutation is in a part of the DNA that does not code for protein.
• Beneficial. Rarely, a mutation produces a protein that gives an advantage, such as resistance to a disease. Beneficial mutations are the raw material that natural selection can favor.

The key idea is that mutation creates new alleles: it is the original source of the genetic variation that meiosis and fertilization then shuffle (see meiosis and sources of variation).

Biotechnology: using genetic knowledge

Humans have long used genetics to change organisms, and the MCAS expects you to describe two approaches and evaluate them:

• Selective breeding (artificial selection). Choosing organisms with desired traits and breeding them together, so the traits become more common over generations. This is how crops, livestock, and dog breeds were developed. It works only with variation that already exists.
• Genetic engineering. Directly changing an organism's DNA, often by inserting a gene from another species. Examples include bacteria engineered to make human insulin, and crops engineered for pest resistance. Unlike selective breeding, it can move genes between species and produce a result in one generation.

When asked to evaluate biotechnology, give a balanced answer: a benefit (higher yields, disease resistance, producing medicines) and a concern (effects on ecosystems, ethical questions, or reduced genetic diversity). This kind of evidence-based, balanced reasoning is exactly what the science practices reward.

Try this

Q1. Define a mutation and state one possible cause. [2]

• Cue. A mutation is a change in the DNA base sequence; it can occur during DNA replication or be caused by a mutagen such as radiation or certain chemicals.

Q2. Explain why mutation is important for evolution. [2]

• Cue. Mutation is the only source of brand-new alleles (new genetic variation), which provides the raw material that natural selection can act on.