Cells and heredity

Ages 13 to 17 Read alone · about 50 minutes

Read together

All living things are made of cells. A cell has a membrane that controls what goes in and out, cytoplasm where chemical reactions happen and, in plants and animals, a nucleus that holds DNA. Mitochondria release energy from food.

DNA is a long molecule that carries instructions for building and running a living thing. A gene is a section of DNA that helps determine a trait. In 1953, James Watson and Francis Crick described its double-helix shape, using X-ray images made by Rosalind Franklin and Maurice Wilkins.

Heredity was first studied carefully by Gregor Mendel, an Augustinian friar in what is now the Czech Republic. In the 1860s, he crossed pea plants and counted their traits. He found patterns in how traits pass from parents to offspring.

Do it

1. Draw a plant cell and an animal cell and label the main parts. What parts does only the plant cell have (cell wall, chloroplasts)?
2. Try a simple genetics model: in pea plants, tall (T) is dominant over short (t). Cross Tt with Tt on a Punnett square. What fraction of offspring are short?
3. Extract DNA from a strawberry with a grown-up: mash it with water, salt and a little dish soap, filter, then gently pour cold rubbing alcohol on top. White strands appear at the boundary.
4. List three of your own traits and think: which might depend on genes, and which on environment?

Talk about it

• Why was Mendel's careful counting important?
• What is the difference between a gene and a trait?

For the grown-up

Genetics raises important questions about health, identity and ethics. Mendel was a Christian friar and scientist, and his work shows that faith and careful science can go together. Avoid pushing a view of what traits “should” be; every person has inherent dignity.

Mark as done

Next lesson →

Where this comes from

• NGSS Lead States, Next Generation Science Standards: For States, By States (National Academies Press, 2013), performance expectation HS-LS3-1 (ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits)
• Gregor Mendel, “Versuche über Pflanzen-Hybriden” (Experiments on Plant Hybridisation), Verhandlungen des naturforschenden Vereines in Brünn (1866)
• J. D. Watson and F. H. C. Crick, “Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid”, Nature 171 (1953): 737 to 738
• Brenda Maddox, Rosalind Franklin: The Dark Lady of DNA (HarperCollins, 2002)

Written with AI assistance and checked against the sources listed. Please read it before sharing it with a child.