Genes, chromosomes and inheritance
Where DNA is kept, what genes and chromosomes are, how DNA is copied and how features are passed on. With a coin-toss inheritance experiment.
Read
In plant and animal cells, DNA is kept in the nucleus, packed into chromosomes. A chromosome is a thread made of protein and one very long DNA molecule.[1][4]
Human cells have 46 chromosomes in 23 pairs. One of each pair comes from each biological parent.[4]
A gene is a section of DNA that is a basic unit of heredity. Many genes are the instructions for building a protein. Humans have about 20,000 genes.[3][1]
DNA has four bases, A, T, C and G. A always pairs with T and C with G, so one strand of the double helix fixes the order of the other.[1]
When a cell divides, the two strands separate and each is used as a pattern to build a new partner strand. That way every new cell gets a copy of the DNA.[1][2]
A gene can come in slightly different versions, called alleles. You have two copies of each gene, one from each parent. These small differences help make each person unique.[3][5]
Try it: Coin-toss babies
You need
- Two coins per pair of pupils
- A pencil and the tally table
- Optional: stickers to mark the coins 'B' (heads) and 'b' (tails)
Safety
Toss coins gently on the table, not in the air near faces. Coins are small: keep them away from very young children.
What to do
- Each coin is one parent. Both parents have two alleles for one gene: B and b. Heads means the parent passes on B, tails means b.
- Predict: out of 20 'babies', how many will be BB, Bb and bb?
- Toss both coins together. Write down the pair you get (heads + tails counts as Bb, in either order).
- Repeat until you have 20 babies. Use the same coins and the same way of tossing each time: that keeps it fair.
- Add up your tallies. Then add the results of the whole class. Which is closer to your prediction: your 20 tosses or the class total?
What happens, and why?
Each parent passes on one of its two alleles, chosen by chance, like a coin toss. For two Bb parents, a quarter of the babies are expected to be BB, half Bb and a quarter bb (1:2:1). Small samples wander away from this; bigger samples, like the class total, usually come closer.[5][3]
Play: DNA, gene or chromosome?
Read each clue. Does it describe DNA, a gene or a chromosome?
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 15–16