Unraveling the Mystery of Lactose Tolerance
Complete each simulation to explore the concept, then move on. Write your answers on your paper worksheet.
★
Do Now — vocabulary matching
Round 1 of 2 — 12 terms from the full set of 24
Click a term on the left, then click its matching definition on the right. Complete all 12 pairs to unlock the Bonus Round!
Terms
Definitions
Round 1 complete!
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⚡
Bonus Round — vocabulary matching
Round 2 of 2 — the remaining 12 terms from the full set
Click a term on the left, then click its matching definition on the right. Match all 12 bonus terms to finish the warm-up!
Terms
Definitions
All 24 terms matched!
Outstanding — you know your vocabulary! Time to start the simulations.
1
System failure & homeostasis
See how the presence or absence of lactase affects the whole system
Toggle lactase on and off to observe the cascade effect through the digestive and circulatory systems.
LCT gene
Expressed
→
Lactase enzyme
Active
→
Lactose digested
Broken down
→
Circulatory system
Nutrients delivered
→
Homeostasis
Maintained
Lactase production:
Check your understanding
0 of 4 answered
i. What is homeostasis?
AThe process of breaking down food in the stomach
BThe maintenance of stable internal conditions in an organism despite external changes
CThe movement of nutrients through the bloodstream
DThe production of enzymes by the pancreas
ii. When lactase is absent, what happens to undigested lactose in the large intestine?
AIt is absorbed directly into the bloodstream as-is
BIt is broken down by stomach acid
CBacteria ferment it, producing CO₂ gas and acids that cause bloating and discomfort
DIt is stored in the liver for later use
iii. Which two body systems must interact for nutrients from digestion to reach body cells?
ANervous system and muscular system
BDigestive system and circulatory system
CEndocrine system and immune system
DRespiratory system and skeletal system
iv. In a person with lactose intolerance, why does lactase deficiency count as a failure of homeostasis?
ABecause their DNA is damaged beyond repair
BBecause they cannot produce any proteins at all
CBecause the body cannot properly break down and absorb a nutrient, disrupting its stable internal environment
DBecause the circulatory system stops transporting blood
Question 1
Use evidence from the model to explain how the inability of Control Regions 1 and 2 to interact — preventing LCT gene expression — impacts the digestive and circulatory systems' ability to maintain homeostasis.
2a
Why digestion is essential
Explore why large molecules cannot enter cells directly
Click each molecule to try to move it across the cell membrane. Observe what happens.
Cell Membrane
Outside cell
Lactose (large)
Glucose (small)
Inside cell
Click the molecules above to attempt membrane crossing
Check your understanding
0 of 4 answered
i. Why can't large food molecules like lactose cross the cell membrane directly?
ABecause they are negatively charged and the membrane repels them
BBecause the cell membrane acts as a selective barrier — only small molecules can diffuse through
CBecause large molecules dissolve in water and wash away
DBecause the stomach acid destroys them before they reach the membrane
ii. After lactose is broken down by lactase, which small molecules enter the bloodstream?
AFatty acids and glycerol
BAmino acids and water
CGlucose and galactose
DCarbon dioxide and water
iii. What process allows small molecules to move from the intestine into the blood after digestion?
AActive transport only — it always requires energy
BDiffusion and transport across the intestinal cell membrane into the circulatory system
COsmosis — water pressure pushes them through
DEndocytosis — the cell engulfs them whole
iv. Which best explains why digestion is classified as an "essential life function"?
ABecause it makes food taste better and increases appetite
BBecause it only occurs in mammals with stomachs
CBecause without it, cells cannot receive the energy and materials needed to survive and maintain homeostasis
DBecause it produces oxygen for cellular respiration
Question 2a
Explain why digestion is considered an essential life function.
2b
The role of proteins
Sort protein types into their correct functional categories
Click each protein card to place it in the correct category. All proteins have a specific job in keeping the organism alive.
Lactase
Insulin
Amylase
Glucagon
Pepsin
Collagen
Keratin
Estrogen
🔬 Enzymes — catalyze reactions
📡 Hormones — cell signaling
🏗️ Structural — body framework
Other functions
Check your understanding
0 of 4 answered
i. What makes enzymes unique compared to other proteins?
AThey carry oxygen in the blood
BThey catalyze (speed up) specific chemical reactions without being consumed in the process
CThey form the structural framework of bones and tendons
DThey send signals between cells through the nervous system
ii. Insulin is a hormone produced by the pancreas. What is the primary role of hormones?
ATo break down food molecules into smaller pieces
BTo provide structural support to muscles and skin
CTo regulate and signal cells — coordinating responses across the body
DTo store genetic information for future generations
iii. A protein must have a specific 3D shape to function. What happens if a protein's shape is altered?
AIt becomes a different type of protein with new functions
BIt loses its ability to carry out its specific function — it becomes non-functional
CIt works faster because the new shape is more efficient
DIt turns into DNA and gets stored in the nucleus
iv. Which statement best explains the relationship between proteins and essential life functions?
AProteins are only needed during growth and can be absent in adults
BProteins provide energy for the body, replacing carbohydrates and fats
CProteins are the molecular workers that carry out and regulate virtually every chemical reaction and structural function needed for life
DProteins are only found in muscle cells and play no role in digestion
Question 2b
What is the role of proteins in the ability of an organism to carry out digestion and/or other essential functions required for life?
2c
DNA → RNA → Protein
Step through the central dogma of molecular biology
Click "Next step" to walk through how DNA directs protein production. Then try the mutation toggle to see what happens when the code changes.
DNA: ATG — GGT — TAG — ACT — CAT — GAG — AAT
1
DNA — the blueprint
The LCT gene sequence in the nucleus serves as the master code for building lactase.
2
Transcription — DNA → mRNA
RNA polymerase reads the DNA and makes a messenger RNA (mRNA) copy to carry the instructions out of the nucleus.
3
Translation — mRNA → protein
Ribosomes read the mRNA codons and assemble amino acids into the lactase protein chain.
4
Protein folds and functions
The amino acid chain folds into the specific 3D shape of lactase — it can now break down lactose molecules.
Check your understanding
0 of 5 answered
i. What is the correct order of the central dogma of molecular biology?
AProtein → RNA → DNA
BRNA → DNA → Protein
CDNA → RNA → Protein
DDNA → Protein → RNA
ii. During transcription, what does RNA polymerase produce?
AA copy of the entire chromosome
BA messenger RNA (mRNA) strand that carries the gene's code out of the nucleus
CA completed protein chain ready to fold
DA double-stranded DNA copy identical to the original
iii. During translation, what reads the mRNA and assembles the protein?
AThe nucleus
BDNA polymerase
CRibosomes
DThe cell membrane
iv. If a mutation changes a codon in the LCT gene's DNA sequence to an early stop codon, what is the most likely outcome?
AThe protein is produced faster than normal
BA truncated, non-functional lactase protein is made — translation stops too early
CThe mutation is automatically corrected by the ribosome
DMore mRNA is produced to compensate
v. Why must a protein fold into a specific 3D shape after translation?
ASo it can fit inside the nucleus for storage
BBecause the protein's shape determines its function — it must fit its target molecule like a lock and key
CSo it can be packaged and sent out of the cell as waste
DTo protect the mRNA from degradation
Question 2c
Describe the role of DNA in the production of proteins that carry out the essential functions of life.
3a
One blueprint, many cell types
Explore the paradox of cell differentiation
All these cells came from the same embryo and carry identical DNA. Click each cell type to explore which genes are expressed.
Intestinal cell
Produces lactase
Muscle cell
No lactase
Nerve cell
No lactase
Liver cell
No lactase
Cardiac cell
No lactase
Stem cell
All DNA present
Click a cell type above to see which genes are switched on.
Check your understanding
0 of 3 answered
i. Do all cells in a human body contain the same DNA?
ANo — each cell type has a different genome suited to its function
BNo — only stem cells contain the complete genome
CYes — every cell contains the same complete DNA, because they all descended from the same fertilized egg
DYes — but only for the genes that are actively being used
ii. If muscle cells and intestinal cells both have the LCT gene, why does only the intestinal cell produce lactase?
ABecause the LCT gene is only switched ON in intestinal cells — gene expression differs between cell types
BBecause the LCT gene is deleted from muscle cells during development
CBecause muscle cells do not have ribosomes
DBecause lactase is only needed for muscle contraction
iii. Which term describes the process by which a cell develops a specialized structure and function from a stem cell?
AMutation
BReplication
CDifferentiation
DTranscription
Question 3a
Write a question that could be asked to clarify the role of DNA and gene expression in the differentiation of cells.
3b
The genetic switchboard
Toggle coding and non-coding DNA to control cell specialization
Flip the switches to see how non-coding (regulatory) DNA controls which genes get expressed in different cell types.
Control Region 1 (non-coding DNA switch)
Control Region 2 (non-coding DNA switch)
LCT Gene (coding DNA — lactase blueprint)
✅ Both control regions active → LCT gene expressed → Lactase produced
Check your understanding
0 of 4 answered
i. What is the role of non-coding DNA in gene expression?
AIt codes for structural proteins like collagen
BIt acts as a regulatory switch, controlling whether coding regions are turned on or off
CIt stores backup copies of genes in case the originals are damaged
DIt is transcribed into mRNA to produce enzymes
ii. In the switchboard simulation, what happens when Control Region 1 is switched OFF?
AMore lactase is produced to compensate
BThe LCT gene is permanently deleted from the DNA
CThe LCT gene cannot be activated, so lactase production stops or is greatly reduced
DControl Region 2 automatically takes over and keeps the gene on
iii. Why do intestinal cells produce lactase but liver cells do not, even though both have the LCT gene?
AThe LCT gene was deleted from liver cells during development
BThe non-coding control regions for LCT are only active in intestinal cells, so only they express the gene
CLiver cells do not contain ribosomes needed for protein synthesis
DLactase is produced in the liver and shipped to the intestine
iv. What does the term "gene expression" mean?
AThe physical appearance of an organism determined by environment alone
BThe mutation of a gene to create a new allele
CThe process by which the information in a gene is used to produce a functional product, such as a protein
DThe replication of DNA before cell division
Question 3b
What is the effect of coding and non-coding DNA on the production of specialized cells that carry out specific essential life functions?
4
Passing the blueprint — inheritance
Build a Punnett square with the LCT alleles
Select the alleles each parent passes to their sex cell, then see the possible genotypes of offspring in the Punnett square.
L = lactase persistence allele (dominant)
l = lactase non-persistence allele (recessive)
l = lactase non-persistence allele (recessive)
| L | L | |
|---|---|---|
| L | LL | LL |
| l | Ll | Ll |
Check your understanding
0 of 4 answered
i. How many chromosomes does a human sperm or egg cell (gamete) contain?
A46 chromosomes (2n)
B23 chromosomes (n) — half the normal amount
C92 chromosomes — double to prepare for fertilization
D1 chromosome — only the one containing the LCT gene
ii. Two parents are both heterozygous for lactase persistence (Ll × Ll). What fraction of their offspring would be expected to be lactose intolerant (ll)?
A0/4 — they cannot have a lactose intolerant child
B2/4 — half the offspring will be intolerant
C1/4 — one in four offspring is expected to be ll (intolerant)
D4/4 — all offspring will be intolerant if both parents carry the recessive allele
iii. The L allele (lactase persistence) is dominant over l. What does this mean for a person with genotype Ll?
AThey will be lactose intolerant because they carry the recessive allele
BThey will be lactose tolerant — the dominant L allele is expressed and drives lactase production
CThey will express both traits equally, being partially intolerant
DTheir children will all be LL
iv. During fertilization, a sperm (carrying allele L) joins an egg (carrying allele l). What is the resulting zygote genotype and chromosome number?
ALL with 23 chromosomes
Bll with 46 chromosomes
CLl with 46 chromosomes — one allele from each parent, restoring the full 2n genome
DLl with 23 chromosomes
Question 4
Construct a model (describe in words, or reference the Punnett square above) to illustrate how genetic material is passed from each parent to offspring. Include specific cells and the amount of genetic material present.
5
Epigenetics — the environmental padlock
Add or remove methyl groups to see how environment silences genes
Click "Add methyl group" on each control region to lock it. Observe how methylation blocks the LCT gene from being expressed.
🔓
Control Region 1
No methyl group
🔓
Control Region 2
No methyl group
LCT Gene
Can be expressed
Control regions free → can interact → LCT gene ON → Lactase produced ✅
65% of adults worldwide become lactose intolerant, even though all humans are born tolerant. Methylation is one key mechanism.
Check your understanding
0 of 4 answered
i. What is the key difference between a genetic mutation and an epigenetic change like methylation?
AMutations are caused by the environment; epigenetic changes are inherited from parents
BMutations change the DNA sequence itself; methylation changes how genes are expressed without altering the sequence
CMutations only affect non-coding DNA; methylation only affects coding DNA
DThere is no difference — both permanently destroy the gene
ii. Approximately what percentage of adults worldwide become lactose intolerant, even though all humans are born lactose tolerant?
AAbout 10%
BAbout 35%
CAbout 65%
DAbout 95%
iii. In the epigenetics model, methyl groups attach to Control Regions 1 and 2. What is the direct result?
AThe LCT gene is physically cut out of the chromosome
BExtra copies of the LCT gene are made
CThe control regions cannot interact to switch on the LCT gene, permanently halting lactase production
DThe mRNA for lactase is produced faster than normal
iv. Which statement best supports the claim that environmental factors influence gene expression?
AAll organisms with the same genotype will always have identical traits regardless of where they live
BMethyl groups from the environment attach to DNA over time, altering which genes are expressed — the same genome can produce different traits in different environments
COnly coding DNA is affected by environmental factors; non-coding DNA is immune
DEnvironmental factors only change gene expression in bacteria, not in humans
Question 5
Based on the model, make and defend a claim that explains the influence of methylation caused by environmental factors on the expression of the LCT gene.
6
Science & technology meet genetics
Identify the right tool for identifying and treating genetic conditions
For each scenario, select the most appropriate scientific tool or intervention.
🔍 Identify — finding the cause
A patient has a rare disorder. Which tool best locates the genetic variant responsible?
DNA sequencing
X-ray imaging
Blood pressure test
🛠️ Intervene — treating the condition
A person has a non-functioning LCT gene. Which intervention could help?
Enzyme supplements
CRISPR gene editing
Vitamin D supplements
Check your understanding
0 of 4 answered
i. What does DNA sequencing allow scientists to do?
ADirectly edit genes inside a living organism
BRead the exact order of nucleotide bases in a DNA strand, locating specific variants and disease-causing genes on chromosomes
CProduce proteins in a test tube without using cells
DMeasure the amount of a protein produced by a cell
ii. CRISPR gene editing is described as a genetic "intervention." What makes it different from enzyme supplements as a treatment?
ACRISPR is cheaper and easier to administer than enzyme supplements
BCRISPR targets the root cause by editing the genetic code itself, while enzyme supplements only manage symptoms
CEnzyme supplements edit DNA while CRISPR only replaces missing proteins
DThere is no difference — both treatments work by inserting new genes
iii. A researcher wants to find which specific chromosome carries a variant causing a rare digestive disorder. Which technology is most useful?
ABlood pressure monitoring
BMRI brain scan
CWhole genome DNA/RNA sequencing
DUrine pH testing
iv. How does understanding the genetic code at a molecular level allow scientists to develop targeted treatments?
AIt allows them to change the patient's diet without any medical intervention
BIt allows them to predict the weather patterns that cause genetic disorders
CKnowing the exact location and function of a gene lets scientists design precise tools — like CRISPR or targeted drugs — to correct or compensate for the specific defect
DIt allows scientists to replace the entire genome with a healthy one
Question 6
How are advances in science and technology making it possible to identify the causes of some genetic disorders and develop solutions or treatments?
7
The shifting value of a trait
See how selective advantage changes with environment
Slide between ancestral and modern environments to see how the selective advantage of the LCT allele changes.
Food availability
Very limited
Only local food sources
Medical intervention
None available
No treatment for symptoms
Selective advantage of LCT allele
Very High
Critical for survival — dairy was an essential caloric source
In ancestral environments, lactose-tolerant individuals could extract vital energy from milk — a critical advantage when food was scarce and no alternatives existed.
Check your understanding
0 of 4 answered
i. In ancestral human populations with limited food sources, which best describes the selective advantage of the LCT allele?
AIt was a minor advantage — dairy was rarely consumed by any humans
BIt was highly advantageous — lactose-tolerant individuals could extract critical calories from milk when other food was scarce
CIt was a disadvantage — dairy caused weight gain that slowed people down
DIt provided no advantage — diet had no effect on reproductive success
ii. Why is the selective advantage of the LCT allele decreasing in modern human populations?
ABecause modern humans no longer keep dairy animals
BBecause alternatives like plant-based milks, enzyme supplements, and global food access reduce the survival necessity of being able to digest lactose
CBecause the LCT allele has mutated and no longer functions
DBecause natural selection no longer operates in human populations
iii. Natural selection acts on traits. What does a "selective advantage" require to affect a population over generations?
AThe trait must be learned and taught to offspring
BThe trait must be heritable AND increase reproductive success in the current environment
CThe trait must appear in 100% of the population within one generation
DThe trait only needs to be heritable — the environment is irrelevant
iv. A trait that was once highly advantageous may become neutral or even disadvantageous as environments change. Which concept does this best illustrate?
AGenetic drift — random changes in allele frequency
BMutation — a new allele arises spontaneously
CContext-dependent selection — the value of a trait is always relative to the current environment and available resources
DGene flow — alleles moving between isolated populations
Question 7
Construct an explanation comparing the selective advantage of the lactose tolerant allele in ancestral human populations to modern human populations with access to medicine and different foods.
8a
Pigeon lice & natural selection
Run the 48-month selection simulation
Choose a pigeon color, then run the simulation to watch how lice color changes over 48 months due to directional selection by preening.
Select pigeon:
Select a pigeon color and run the simulation to see how lice luminosity changes over 48 months.
Check your understanding
0 of 4 answered
i. In the pigeon lice experiment, what acts as the selective pressure that drives changes in lice color?
ATemperature changes in the environment
BRandom genetic mutations in the lice population
CPreening behavior — the pigeon removes lice that are visually contrasting with its own feather color
DCompetition between lice for food resources on the pigeon
ii. On white pigeons, what change in lice luminosity (brightness) do you observe over 48 months, and why?
ALuminosity decreases — darker lice blend in better on white feathers
BLuminosity increases — lighter lice survive preening more often and pass on their genes, shifting the population toward higher brightness
CLuminosity stays flat — white pigeons do not preen
DLuminosity increases then decreases in a cycle
iii. The graph shows that lice on black pigeons have decreasing luminosity over 48 months. What is the best explanation?
ABlack pigeons produce a chemical that bleaches lice over time
BLighter lice are more visible on black feathers and are preferentially removed by preening — darker lice survive and reproduce, lowering average luminosity
CLice naturally darken with age regardless of their host
DThere are fewer lice on black pigeons so the sample size is too small
iv. This pigeon lice study is evidence that natural selection is not random. What does this mean?
ALice choose to change their color voluntarily to match their host
BThe change in lice color is caused by random genetic drift with no environmental cause
CThe direction of change is determined by the specific selective pressure (pigeon color) — individuals better suited to their environment consistently survive and reproduce more
DAll lice eventually evolve to the same color regardless of host
Question 8a
Use qualitative and quantitative data from the simulation to explain the variation and distribution of body color in the lice populations on dark and/or light-colored birds over the duration of the study.
8b
The gray control — stabilizing selection
Explain why gray pigeon lice luminosity stays flat
The gray pigeon is a control. Click each lice color below to see its probability of being removed by the gray pigeon's preening.
☁️ Light lice on gray pigeon
🌑 Dark lice on gray pigeon
Select a lice color above to see the selection pressure.
Result: On gray pigeons, light and dark lice are removed at equal rates. Neither color has an advantage, so the population luminosity stays near zero — stabilizing selection.
Check your understanding
0 of 4 answered
i. Why was the gray pigeon chosen as the control group in this experiment?
ABecause gray pigeons do not preen, removing any selection pressure
BBecause its intermediate color makes both light and dark lice equally visible — neither color has a selective advantage, providing a neutral baseline
CBecause gray pigeons have the most lice, making data collection easier
DBecause gray pigeons live in a different habitat and are not affected by selection
ii. On gray pigeons, lice luminosity stays near zero for all 48 months. What type of selection does this represent?
ADirectional selection — the population shifts toward one extreme
BDisruptive selection — both extremes are favored simultaneously
CStabilizing selection — intermediate traits are maintained because no extreme has an advantage
DArtificial selection — humans are choosing which lice survive
iii. What would you predict about lice luminosity on gray pigeons if the experiment ran for 10 years instead of 4?
ALuminosity would eventually increase — gray is actually closer to white
BLuminosity would remain near zero — since neither extreme has a selective advantage, the selection pressure does not change over time
CLuminosity would decrease sharply — lice always evolve to be darker
DLuminosity would become impossible to measure
iv. The conclusion of the pigeon lice study states: "Variation and distribution of expressed traits in a population are the direct result of natural selection, not random chance." Which data best supports this conclusion?
AAll three pigeon colors showed the same change in lice luminosity over time
BLice on white pigeons became lighter, lice on black pigeons became darker, and lice on gray pigeons stayed stable — each population changed predictably based on its specific selective pressure
CLice color changed randomly on all three pigeon types with no clear pattern
DOnly the gray pigeon showed any change in lice color
Question 8b
The gray pigeon served as a control for the experiment. Use the data to construct an explanation for the distribution of the relative luminosity of the lice present on gray pigeons over 48 months.
Worksheet complete!
You've explored lactose tolerance from molecular blueprints to population-level natural selection.