--- title: "Where are the instructions?" subtitle: "Year 10 Biology · Genetics · Lesson 1" --- # Where are the instructions? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** Unwound, the DNA in one of your cells would be about two metres long. It fits in a nucleus a hundredth of a millimetre across. :::teacher-note **In one sentence:** Students relate DNA, chromosomes, genes and alleles by size and meaning, and explain chromosome pairs (AC9S10U01, node 1, a hinge node). **Students should be able to say:** I can put the cell, nucleus, chromosome, DNA and gene in order of size. I can define gene and allele. I can explain why chromosomes come in pairs. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **Put these in order from biggest to smallest: gene, chromosome, nucleus, DNA molecule.** ☐ Chromosome, nucleus, gene, DNA ☐ Nucleus, chromosome, DNA molecule, gene (a section of it) ☐ Gene, chromosome, DNA, nucleus ☐ Nucleus, chromosome, gene, DNA My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** Nucleus, then chromosome (one long, coiled DNA molecule), then a gene, which is a short section of that DNA. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: DNA, genes and alleles :::keep-together ### Words **Match each word to its meaning.** A. One long DNA molecule, tightly coiled B. One version of a gene C. A section of DNA that codes for one protein D. A long molecule carrying the coded instructions {{columns 60% 40%}} {{rows 1}} | Part | Letter | |---|---| | `DNA` | | | `Chromosome` | | | `Gene` | | | `Allele` | | ::: :::teacher-note **Answer:** DNA → D. A long molecule carrying the coded instructions; Chromosome → A. One long DNA molecule, tightly coiled; Gene → C. A section of DNA that codes for one protein; Allele → B. One version of a gene ::: :::keep-together ### Alleles **One gene decides your blood group, yet people have blood group A, B, AB or O. How?** ☐ People have different alleles (versions) of the same gene ☐ Only some people have the gene ☐ The environment decides ☐ There is a separate gene for each blood group ::: :::teacher-note **Answer:** People have different alleles (versions) of the same gene ::: :::keep-together ### Pairs **Your body cells have 46 chromosomes. Why are they described as 23 pairs?** ☐ One of each pair came from each parent, and the two carry the same genes (perhaps different alleles) ☐ Boys and girls have different chromosomes ☐ Pairs are easier to count ☐ Each chromosome copies itself ::: :::teacher-note **Answer:** One of each pair came from each parent, and the two carry the same genes (perhaps different alleles) ::: :::keep-together ### Genotype and phenotype **Someone has the blood group alleles A and O, and their blood group is A. Which is their genotype and which their phenotype?** ☐ Genotype: the chromosome the gene is on. Phenotype: the gene ☐ Both are 'blood group A': the words mean the same thing ☐ Genotype: the alleles A and O. Phenotype: blood group A, the characteristic that shows ☐ Genotype: blood group A. Phenotype: the alleles A and O ::: :::teacher-note **Answer:** Genotype: the alleles A and O. Phenotype: blood group A, the characteristic that shows ::: :::typical ## Elaborate: from code to characteristic :::keep-together **Put the steps in order.** Groups: 1st, 2nd, 3rd, 4th - A gene's sequence of bases (A, T, C, G) is read: {{field-15}} - The cell builds a protein from that code: {{field-15}} - The protein does a job (a pigment, an enzyme, a structure): {{field-15}} - A characteristic appears (such as eye colour): {{field-15}} ::: :::teacher-note **Answer:** A gene's sequence of bases (A, T, C, G) is read → 1st; The cell builds a protein from that code → 2nd; The protein does a job (a pigment, an enzyme, a structure) → 3rd; A characteristic appears (such as eye colour) → 4th ::: ::: :::wider ## Elaborate: the same code everywhere :::keep-together **A nerve cell and a skin cell from the same person have the same DNA. Why do they look and work so differently?** ☐ Nerve cells have extra genes ☐ Skin cells lose most of their DNA ☐ Each cell uses (switches on) different genes ☐ They have different chromosomes ::: :::teacher-note **Answer:** Each cell uses (switches on) different genes ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - **DNA** carries coded instructions as a sequence of bases (A, T, C, G). - A **chromosome** is one long DNA molecule, coiled; humans have 46, in 23 pairs (one of each pair from each parent). - A **gene** is a section of DNA coding for a protein; **alleles** are different versions of one gene. - **Genotype:** the alleles you have (such as A and O). **Phenotype:** the characteristic that shows (blood group A). ## Exit ticket :::keep-together **What's the difference between a gene and an allele?** {{lines-3}} ::: :::teacher-note **Answer:** A gene is a section of DNA coding for a protein; an allele is one version of that gene. :::