## Essential question How can environment and lifestyle affect traits and survival, and when can those effects be passed to the next generation?

## Vocabulary - Gene: a segment of DNA that contains instructions for making a product (often a protein). - Trait: a characteristic (for example, eye color, height range, enzyme function). - Gene expression: how much a gene is used to make its product. You can think of it as genes being turned up, down, on, or off. - Mutation: a change in DNA. - Somatic cell: a body cell (skin, muscle, liver). - Germ cell: cells that make eggs or sperm.

## Three ways environment and lifestyle matter (and how to talk about them accurately)

1) Environment can change gene expression - Example: Sunlight can increase melanin production (tanning). The DNA sequence does not change, but cells use some genes more. - Example: Exercise changes which genes muscle cells use more often.

2) Environment can cause mutations - Some exposures (like UV light or chemicals in tobacco smoke) can damage DNA. - If a mutation happens in a body cell, it affects only that person. - If a mutation happens in an egg or sperm, it can be inherited.

3) Environment changes survival - The same inherited trait can be helpful in one environment and harmful in another. - Over many generations, traits that improve survival and reproduction can become more common in a population.

Important accuracy point: lifestyle choices do not rewrite your inherited DNA like editing a book. They mostly change which genes are used, and they change the conditions your body faces.

## Quick examples tied to the standard

- PKU (phenylketonuria): A person can inherit a gene variant that affects how they break down phenylalanine. A careful diet can reduce harm. The gene is inherited, but environment (diet) changes the outcome.

- UV exposure and skin: Sunlight can increase melanin (a gene expression response). UV can also damage DNA in skin cells. That damage is usually not inherited, but it can increase the risk of skin cancer for the person.

- Sickle cell trait and malaria (population example): In regions with malaria, having one sickle cell allele can reduce severe malaria risk. In regions without malaria, that benefit is smaller, and sickle cell disease (two alleles) is harmful. This shows how environment can affect survival and which traits become common.