HS-LS3-2: Where Genetic Variation Comes From
Also called NGSS HS-LS3-2 · Topic: Inheritance and Variation of Traits · Life Science
The Official Wording
Make and defend a claim based on evidence that inheritable genetic variations may result from (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and/or (3) mutations caused by environmental factors.
Clarification statement: Emphasis is on using data to support arguments for the way variation occurs.
Assessment boundary: Assessment does not include the phases of meiosis or the biochemical mechanism of specific steps in the process.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-LS3-2 Means in Plain English
Students make a claim about where new inherited differences come from and defend it with data. They weigh three sources: meiosis reshuffling chromosomes into new combinations, copying errors when DNA replicates that a cell survives, and mutations triggered by things like ultraviolet light or certain chemicals.
Students do not need the phases of meiosis or the chemistry of DNA repair. Only changes in egg or sperm cells pass to offspring. This builds on HS-LS3-1 and feeds HS-LS4-2, where variation becomes the raw material of evolution.
HS-LS3-2 I Can Statements
- I can name three sources of new genetic variation.
- I can support a claim about mutations with experimental data.
- I can explain why only changes in sex cells are inherited.
HS-LS3-2 Worked Example
An experiment with a yeast strain that cannot repair UV damage, used as evidence that the environment can change DNA.
Does sunlight damage the DNA of yeast cells that cannot repair it?
Set It Up: Agar plates spread with UV-sensitive yeast, cardboard masks that cover half of each plate, a timer and a sunny spot outdoors.
- Cover half of each plate with a cardboard mask and remove the lids.Masked half is the control
- Expose plates to midday sun for 0, 15, 30 and 60 seconds, then replace the lids.One plate per exposure time
- Keep the plates at room temperature for two days and count colonies on each masked half.Masked halves: about 120 colonies each
- Count colonies on the exposed halves.0 s: 118. 15 s: 74. 30 s: 31. 60 s: 6
- Compare with a normal yeast strain treated the same way.Normal strain barely drops
The longer the sensitive yeast sat in sunlight, the fewer colonies grew on the exposed side, while masked halves and normal yeast were barely affected.
Why it works: Ultraviolet light damages DNA, and cells that cannot repair the damage die or carry mutations, which is evidence that environmental factors can change genetic material.
Common Mistakes with HS-LS3-2
Thinking all mutations are harmful
“Mutations always cause disease”
Try this: Most mutations have no visible effect, some are harmful, and a few help, which is why variation can fuel evolution.
Sunburn mutations get inherited
“A sunburned parent passes skin mutations to the baby”
Try this: Only DNA changes in egg or sperm cells reach the next generation, so mutations in skin cells stay with that person.
Forgetting meiosis makes variation
“Siblings differ only because of mutations”
Try this: Meiosis shuffles each parent's chromosome pairs and crossing over swaps pieces, so siblings get different combinations even without new mutations.
Where HS-LS3-2 Fits
Practice HS-LS3-2
Quick Check
- Name the three main sources of new inherited variation.
- Why do two siblings from the same parents look different?
- A skin cell mutates after a sunburn. Can the person's children inherit it?