--- title: "Chromosomes, Genes & DNA" description: "Describe the relationship between chromosomes, genes, and DNA in heredity, including the double helix structure of DNA and the historical roles of Watson, Crick, Franklin, and Wilkins" canonical: https://lightmysky.com/learn/science/chromosomes-genes-and-dna-mt_6aJUzBYGNs source: https://lightmysky.com/learn/science/chromosomes-genes-and-dna-mt_6aJUzBYGNs.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Chromosomes, Genes & DNA Describe the relationship between chromosomes, genes, and DNA in heredity, including the double helix structure of DNA and the historical roles of Watson, Crick, Franklin, and Wilkins Subject: Science · Area: Ecosystems & Habitats · Ages 12 to 13 Page: https://lightmysky.com/learn/science/chromosomes-genes-and-dna-mt_6aJUzBYGNs ## Ready when they can - Explains that a gene is a section of DNA and that chromosomes package DNA with proteins inside a typical human cell's nucleus - Describes how many genes provide instructions for proteins, and explains that several genes and the environment can influence one trait - States that a typical human body cell has 46 chromosomes in 23 pairs, while mature red blood cells have none - Describes the contributions of Watson, Crick, Franklin, and Wilkins to working out DNA structure ## Lesson: Chromosomes, Genes and DNA Human skin cells and nerve cells have a nucleus. Most of their DNA is inside it. The nuclear DNA in a typical human body cell would stretch to about two metres. Chromosomes package DNA with proteins. This packaging becomes especially tight when a cell prepares to divide. A gene is a section of DNA with instructions for a working molecule. Many genes provide instructions for proteins, which build structures or do jobs in cells. One trait can involve several genes and the environment. A chromosome contains many genes, DNA outside genes and packaging proteins. DNA is its material, so a chromosome and its DNA molecule are not separate levels in a size ranking. *(drawing: Two matching DNA stretches: corresponding positions pair A with T, and G with C. These letters show base pairs, not the helix's shape.)* **Example.** A typical human skin cell has 46 chromosomes in 23 pairs, one chromosome of each pair from each biological parent. To count from pairs, multiply by two. Mature human red blood cells have no nucleus and no chromosomes. DNA's usual shape is a double helix: two strands twisted around each other. Sugar and phosphate form the sides of the ladder-like molecule. Pairs of chemical bases form its rungs. The bases have letter names: A pairs with T, and G pairs with C. Franklin and Wilkins studied DNA using X-ray diffraction patterns, which give clues about molecular shape. Watson and Crick used X-ray evidence and other researchers' findings to propose a double helix model in 1953. Watson, Crick and Wilkins received the 1962 Nobel Prize in Physiology or Medicine. Franklin had died before the award. **Recap.** Genes are DNA sections. Chromosomes package DNA with proteins. A typical human body cell has 46 chromosomes in 23 pairs. X-ray evidence helped scientists work out DNA's double helix. *Lesson, questions and flashcards written for this dataset. OpenStax records were studied for scientific background.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Cells Under the Microscope](https://lightmysky.com/learn/science/cells-under-the-microscope-mt_VfA4xo4kUv) ## Opens up - [DNA & Genes](https://lightmysky.com/learn/science/dna-and-genes-mt_0sELh0MYWb) - [Grouping Species Using DNA](https://lightmysky.com/learn/science/grouping-species-using-dna-mt_fqAkSv3cUE) - [Meiosis and Why Gametes Are Haploid](https://lightmysky.com/learn/science/meiosis-and-why-gametes-are-haploid-mt_hvu0bczcfX) - [Variation in Species](https://lightmysky.com/learn/science/variation-in-species-mt_k1HXbEwG8f) - [Predicting Inherited Traits](https://lightmysky.com/learn/science/predicting-inherited-traits-mt_o7FJPDsHiW) - [Genetic Mutation](https://lightmysky.com/learn/science/genetic-mutation-mt_rOqo-8GeKt) - [Megafauna Extinction & De-Extinction](https://lightmysky.com/learn/science/megafauna-extinction-and-de-extinction-mt_tGZ2sMzMGz)