Sources of Genetic Variation

Overview

In this first lesson of the six-lesson unit Variation, Inheritance and Selection, students investigate where genetic variation comes from. They distinguish mutation, meiosis and sexual reproduction, then use examples and evidence to explain how each process can produce differences between individuals.

Learning intentions

• WALT identify sources of genetic variation.
• WALT distinguish mutation, meiosis and sexual reproduction.
• WALT use biological evidence to explain how variation arises.
• WALT communicate ideas using accurate scientific language, symbols and texts.

Success criteria

• I can define mutation, meiosis and sexual reproduction.
• I can explain how each process contributes to genetic variation.
• I can use an example or piece of evidence to support a biological explanation.
• I can distinguish between the origin of a new allele and the reshuffling of existing alleles.

Curriculum links

• Genetic variation in relation to an identified characteristic: describing sources and the nature of genetic variation, and preparing to use gene-tracking methodology.
• Science investigation: using evidence from examples and models to answer a biological question.
• Science capabilities: interpreting patterns and interactions, linking evidence to biological ideas, and communicating with scientific language, symbols and conventions.
• New Zealand Curriculum key competencies: thinking; using language, symbols and texts; and managing self during independent and collaborative work.

Lesson structure (60 minutes)

1. 0–7 min · Hook and prior knowledge. Teacher displays two images of people or organisms showing variation in an identified characteristic, such as blood type, lactose tolerance or flower colour, using the opening comparison and hook question and asks, “How could these differences arise if individuals of the same species have the same basic genes?” Students make an individual prediction, then share one idea with a partner. Teacher records student explanations without correcting them yet.

2. 7–18 min · Direct teaching: key ideas. Teacher uses the concept slides on alleles, mutation, meiosis and sexual reproduction to establish that genetic variation means differences in DNA or alleles within individuals or populations. Explain that mutation can create a new allele; meiosis produces genetically different gametes through crossing over and independent assortment; and sexual reproduction combines alleles from two parents through random fertilisation. Students complete the key-term definitions and a simple cause-and-effect diagram on the genetic variation investigation worksheet.

3. 18–32 min · Evidence investigation. Teacher introduces three evidence examples on the evidence-example slides: a mutation that changes an allele and phenotype, crossing over producing different chromosome combinations, and siblings inheriting different allele combinations from the same parents. Students work in groups of three, with each student becoming the group expert for one process. They read the relevant example on the worksheet and answer: “What is changing?”, “How does the change occur?” and “What evidence supports this explanation?” Groups then teach their process to one another.

4. 32–44 min · Compare and classify. Teacher models the distinction between “creating a new allele” and “rearranging or combining existing alleles”. Students complete the comparison table on the worksheet, classifying statements such as “a DNA base sequence changes”, “homologous chromosomes exchange sections”, “two gametes fuse” and “offspring receive alleles from two parents”. Pairs must justify each classification using the terms mutation, meiosis or sexual reproduction. Teacher checks responses and addresses the misconception that meiosis itself always creates new alleles.

5. 44–54 min · Written explanation. Teacher displays the response structure on the explanation scaffold and worked example: identify the process, describe what happens, link it to genetic variation, and support the explanation with evidence. Students independently answer: “Explain how meiosis contributes to genetic variation in a population.” They then choose either mutation or sexual reproduction for a second, shorter explanation. Teacher conferences with students and prompts precise use of “allele”, “gamete”, “DNA”, “variation” and “offspring”.

6. 54–60 min · Plenary and exit check. Teacher uses the retrieval questions and final summary for a whole-class review. Students complete the final three-question exit check on the worksheet: define mutation; identify the process responsible for crossing over; and explain one way sexual reproduction creates variation. Collect responses to identify needs for Lesson 2.

Resources

• the Sources of Genetic Variation slide deck
• the genetic variation investigation worksheet
• Projector or interactive display
• Whiteboard and coloured pens
• Student exercise books or devices
• Highlighters for identifying evidence and key terms
• Timer

Assessment

• Listen to group explanations and question whether students can distinguish new allele formation from allele reshuffling.
• Check the comparison table and written explanation for accurate use of mutation, meiosis, sexual reproduction, allele, gamete and variation.
• Use the exit check to identify misconceptions, especially the belief that meiosis creates new alleles or that all siblings have identical genetic information.

Differentiation

• Provide a word bank, labelled diagrams and sentence starters such as “Mutation contributes to variation because…” and “During meiosis…”.
• Pair students strategically for the expert investigation and allow students to explain ideas orally before writing.
• For EAL learners, pre-teach the terms with simple definitions and visual representations; accept a labelled diagram alongside written explanations while developing language accuracy.
• Support students requiring additional assistance with a partially completed comparison table. Extend confident students by asking them to explain how a mutation could be harmful, beneficial or have no observable effect, depending on context.