Heredity and Change over Generations
Grade 7 | Science | Unit 07
Teacher's Guide
Learning objectives
- Explain the central ideas of heredity and change over generations using appropriate vocabulary.
- Apply the worked example and justify answers to the practice questions.
- Complete the investigation or design task and identify a limitation of its model or evidence.
Prerequisites: Basic reading, arithmetic, and observation skills.
Suggested time: Two or three 45-minute sessions; extend the activity when needed.
Teaching sequence
- Elicit a prior explanation of the topic and note uncertain vocabulary.
- Discuss the concept section, distinguishing observations, models, and assumptions.
- Work through the example. Ask students to explain each step and check any units.
- Complete the activity, then use the five practice questions as an individual check.
- Review the two vocabulary questions and revisit misconceptions revealed by the answers.
Assessment and differentiation
Use the seven questions in the companion CSV for retrieval practice or a short quiz. Award one point per entry for an accurate answer; accept scientifically equivalent wording. Treat five correct answers as a suggested checkpoint for further review, with both reasoning and activity quality assessed separately. Support students with a labeled diagram, a word bank, or a completed first step. Extend by asking students to change one example condition, predict the effect, and explain a limitation.
Student Worksheet
Concept and helping material
Genes are inherited units of information encoded in DNA. Different versions of a gene are alleles. An organism has a genotype and observable characteristics called its phenotype; environment can also affect phenotype. Simple inheritance models use dominant and recessive alleles, but many traits involve several genes. Mutations introduce genetic variation. Natural selection occurs when heritable differences affect survival and reproduction in a particular environment. Populations change over generations; individuals do not evolve because they need a new trait. Fossils and rock layers provide evidence about past organisms and environments.
Vocabulary
- Allele: A version of a gene.
- Natural selection: Differences in reproductive success associated with heritable traits in a particular environment.
Worked example
In a simplified model, T is dominant to t. Crossing Tt with tt produces two Tt and two tt outcomes in a four-box Punnett square: a 50% chance of each genotype per offspring.
Investigation or design task
Construct the Punnett square and compare its predicted probabilities with 20 coin-pair trials. Explain why a small sample need not exactly match the probabilities.
Practice
- For Tt crossed with tt, what is the chance of tt?
- Does dominant mean more common?
- Can environment affect phenotype?
- Does an individual acquire inherited adaptations because it needs them?
- What can fossils reveal?
Vocabulary retrieval
- Define Allele.
- Define Natural selection.
Reflection
Explain which evidence, calculation, or model supports one of your answers. State a condition under which your explanation might need revision.
Answer Key
- 50% in the simplified single-gene model.
- No. Dominance concerns expression in a heterozygote, not frequency in the population.
- Yes; nutrition and other environmental conditions can affect many characteristics.
- No. Selection acts on heritable variation across generations.
- Evidence of past organisms, environments, and changes over time.
Vocabulary definitions appear above and are also included in the CSV. Activity answers may vary; require a clear method or design, correct use of lesson concepts, and an explicit limitation. Reflection is assessed for reasoning rather than one fixed phrase.
Source Reference
Everything You Need to Ace Science in One Big Fat Notebook, PDF viewer pages 445-486 (1-based). Page numbers refer to this supplied file and may differ from printed page numbers. The source is background reading for the grouped topic. Lesson explanations, examples, and questions are original teaching material; they do not reproduce the book's worksheets or illustrations.