Variation, Grade 7: White Lions, Height Histograms and the Tongue Rolling Myth
A white lion is not an albino, and the photograph normally printed beside that caption proves it.
Look at the nose. A true albino has no melanin anywhere: pink or red eyes, a pink nose, pale lips. The lion in the picture has a dark nose and ordinary amber eyes. It is not an albino, it is leucistic, and the difference is visible in the image itself.
It is also a South African animal. White lions come from the Timbavati and the greater Kruger, and they carry a recessive variant that is part of that population. Calling one an albino throws away both the biology and the story.
Albino or leucistic: the check a learner can do on any photo
| Look at | True albino | Leucistic, like a white lion |
|---|---|---|
| Eyes | Pink or red, because you are seeing blood vessels through an iris with no pigment | Normal colour. Blue, amber or brown |
| Nose and lips | Pink | Dark |
| Paw pads | Pink | Dark |
| Why | No melanin is made at all | Melanin is made, but it does not reach the coat |
That is a thirty-second test and it works on any animal. White peacocks, white squirrels, most "albino" animals in news photographs: check the eyes and the nose before believing the caption.
Where this fits in the curriculum
| Subject | Natural Sciences |
|---|---|
| Grade | 7 |
| Term | 1 |
| Strand | Life and Living |
| Topic | Variation |
| Status | Class activities. Nothing here is formally assessed |
| Marks | The topic revision is 30. Our worksheet is 40 |
What variation actually means
Every member of a species is different from every other member. No two zebras have the same stripes. No two people in a classroom are the same height.
| Continuous variation | Clear-cut variation | |
|---|---|---|
| What it looks like | A smooth range with no gaps | A few separate groups |
| Examples | Height, mass, foot length, hand span | Blood group |
| How you show it | A histogram, in equal ranges | A bar graph of counts |
| Usually caused by | Many genes together, plus the environment | One gene, or very few |
Notice how short that second column is. That is not an accident, and it is the most useful thing on this page.
The class survey traits are mostly myths
Tongue rolling is the most repeated piece of wrong genetics in any school.
It was proposed as a simple inherited trait in 1940 by Alfred Sturtevant. Sturtevant himself publicly withdrew the claim after a 1952 study of identical twins found pairs where one twin could roll and the other could not. Identical twins have identical genes, so a clean single-gene trait cannot do that.
It has been taught in schools ever since anyway.
The same goes for the rest of the classroom set. Hitchhiker's thumb, attached earlobes, a widow's peak, hand clasping: all of them are taught as simple inherited traits and none of them is as clean as the lesson claims.
This is the best free practical in the grade, and it is better than the version printed.
You will find an investigation that has the class count tongue rollers, survey their families, work out percentages and plot a graph, with a box underneath telling the learner that related people are more likely to share the trait.
Run the investigation honestly and the class may produce data that contradicts the box. That is not a failure. That is what the investigation is for, and it beats any confirmed result, because the learner has done the thing science actually does.
And you get to tell them that the scientist who first proposed it read the evidence and changed his mind in public. Most learners have never been told that is allowed.
The one genuinely clean example to use instead is blood group. A, B, AB or O, four clear groups, no in-between, determined by a single gene. If you want a clear-cut trait that survives scrutiny, use that one and leave the tongues alone.
The height survey is the practical worth running
It costs nothing, it takes fifteen minutes, and unlike the tongue rolling survey the result is reliable.
- Measure every learner's height in centimetres, shoes off, heels against a wall
- Group the results into equal ranges, 5 cm wide: 130 to 134, 135 to 139, and so on
- Count how many fall in each range
- Plot the counts as a histogram, with height along the bottom
- Look at the shape
The ranges must all be the same width. A histogram with one 5 cm bar next to one 15 cm bar is not comparing like with like, and the tall bar is tall only because it is wide.
It is worth checking any worked example you hand out for this, because the equal-width rule is followed in some places and broken in others, sometimes within the same topic.
What you should get is a hump in the middle and few at either end. That is the bell shape, and it is what "continuous, controlled by many genes" looks like when you draw it.
A class of 30 gives a lumpy version. A whole grade gives a smooth one. Combine two or three classes if you can, because the improvement is visible and it teaches sample size without a definition.
Inherited or environmental
| Inherited | Environmental |
|---|---|
| Eye colour | A suntan |
| Blood group | Dyed hair |
| Natural hair colour | A tattoo or a scar |
| Nose shape | Muscles built in a gym |
Height belongs in both columns and that is the point of it. Tall parents tend to have tall children, so it is inherited. But a child who is badly fed will not reach the height their genes allowed, so it is environmental too. Most real characteristics are like this, and the two-column table is a simplification a class should be told about.
If it does not work
| Problem | Cause | Fix |
|---|---|---|
| The tongue rolling data does not match the printed claim | Nothing. The claim is not reliable | That is the result. Report it and explain why |
| The histogram has no hump | Too few learners | Combine classes. 30 is lumpy, 90 is smooth |
| One bar is enormous | Unequal ranges | Every range the same width. 5 cm throughout |
| Learners argue about who can roll | Some people learn to fold the tongue with practice | Record what they can do on the first try, and note that this is part of why the trait is not clean |
| Heights are all over the place | Shoes, or heads not level | Shoes off, heels to the wall, a ruler flat on the head |
| A learner insists a white animal is albino | The caption said so | Look at the eyes and the nose. The photo settles it |
Watch the revision table before you set it
The topic revision total is right, but one question has data that cannot be reconciled.
A table describes a single class two ways. By hair colour the girls come to 14 + 7 = 21. By tongue rolling the same girls come to 12 + 6 = 18. The boys are 8 + 6 = 14 one way and 10 + 7 = 17 the other.
The grand total is 35 either way, so three girls and three boys have quietly swapped sides between the two halves of the table.
A learner who cross-checks the columns cannot make it work, and cross-checking is exactly the habit you want. Either fix the numbers before you set it, or set it deliberately and give marks for spotting the problem.
How the 40 marks are made up
| Part | Marks |
|---|---|
| What variation is, and continuous against clear-cut | 8 |
| The height survey and the histogram | 12 |
| Inherited against environmental | 8 |
| Albino against leucistic | 6 |
| Tongue rolling, and reading a claim critically | 6 |
Nothing in this topic is formally assessed. The topic revision is 30 marks and it adds up correctly. Our worksheet is 40 and the split above is ours.
Free worksheet and marking memo
Both free, no sign up, straight to the PDF.
- Learner worksheet, 40 marks, including the histogram to draw and the albino photo check
- Marking memorandum, with what to accept and the five answers that look right and score nothing
Related practicals
- Biodiversity and Classification, Grade 7. Variation between species instead of within one
- Human Reproduction, Grade 7. How the characteristics get passed on in the first place
- Plant Reproduction, Grade 7. The same question, in flowers
What you need to run it
Nothing from us, and we would rather say so than pad the list.
This topic needs a tape measure, a wall, graph paper and a class. We do not sell tape measures, and a school that buys anything for this lesson has been sold something.
If you want to take the inheritance side further than Grade 7 requires, two charts do that well: the Chromosomes wall chart and the Structure of DNA wall chart, both R85. We hold very few of each at the moment, so ask before you plan an order around them.
The rest of our life sciences range is in life sciences, and the charts are in educational wall charts.