Year 10 - Science
Models of single-gene inheritance: Punnett squares
Inheritance, genotype and phenotype
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit covers key genetic terms, single-gene inheritance, and genetic crosses, including probability and ratios. It explores how most traits result from multiple genes and sex determination in humans. The unit also includes interpreting data and using models to solve problems.
Lesson Summary
You will learn to interpret and construct Punnet squares to show the inheritance of alleles of a single gene.
Key Notes
- Most characteristics are influenced by multiple genes, but some are determined by just one.
- An individual will inherit two alleles for each gene, the alleles for a gene may be dominant or recessive.
- A Punnett square models inheritance of alleles showing possible genotypes of offspring as homozygous or heterozygous.
- Punnett squares are used to predict proportion of genotypes/phenotypes, or probability of occurrence in the offspring.
- Each instance of sexual reproduction is independent, so does not affect the probability for subsequent offspring.
Vocabulary To Learn
- Punnett square: A model used to show the inheritance of alleles from parents to offspring.
- gamete: A sex cell (i.e. sperm and egg) that carries half the genetic information required for an individual organism.
- genotype: The combination of alleles that an individual has for each gene.
- ratio: Shows hows how much of one value there is compared to another.
- probability: A measure of the chance or likelihood of an event occurring.
Common Mistakes To Avoid
- A gamete has two alleles, Punnett square has too many alleles for gametes. Also that only four offspring are produced and therefore each will definitely have the genotype and phenotype shown.
3 Quick Questions (With Answers)
1. Explain the scientific idea in this lesson using two key points.
Most characteristics are influenced by multiple genes, but some are determined by just one. An individual will inherit two alleles for each gene, the alleles for a gene may be dominant or recessive.
2. Define this scientific word and use it in context. 'Punnett square'
A model used to show the inheritance of alleles from parents to offspring. Include the word in a full scientific explanation, not as a single label.
3. Correct this common scientific misunderstanding.
Mistake: A gamete has two alleles, Punnett square has too many alleles for gametes. Also that only four offspring are produced and therefore each will definitely have the genotype and phenotype shown. Correction: Model the alleles within gametes so it is clear. Refer to half the gametes having each version, moving away from the idea of divisions of 4.
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