The environment switches genes on and off
- The idea
- Predict
- See it
- Why
- Check
The idea
“If the environment changes a trait, it must have changed the alleles.”
Traits come from genes, so a new trait seems to need new genes. But a gene can stay the same and just be switched off.
The short version
The mistake: If the environment changes a trait, it must have changed the alleles.
What's actually true: The environment changes which genes are expressed, and how much. The alleles themselves stay the same.
- Your genotype is the alleles in your DNA. Day length, food and temperature don't rewrite it. UV light can cause mutations, but that is random damage.
- The environment can change gene expression, meaning which genes are made into mRNA and how much. Short days signal cells through hormones, which turn genes up or down.
- So one genotype can make different phenotypes in different environments.
- Winter doesn't change the alleles the hare passes on. Its young inherit the response to day length and turn white in their own first winter.
On the exam: Same DNA, different conditions, different trait. The environment changed which genes are on.