Genetic inheritance — AQA GCSE Biology
Test yourself on Genetic inheritance with AQA GCSE practice questions.
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Genetic inheritance explained
These ten terms form the vocabulary of inheritance.
Read the full explanation
A gamete is a sex cell, such as a sperm or egg, with a haploid number of chromosomes. A chromosome is a long DNA molecule carrying many genes. A gene is a section of DNA that codes for a protein or characteristic. An allele is a different form of the same gene. A dominant allele is expressed even when only one copy is present, while a recessive allele is expressed only when two copies are present. Homozygous means two identical alleles for a gene; heterozygous means two different alleles. Genotype is the alleles present; phenotype is the observable characteristic. For example, a mouse with genotype Bb is heterozygous and may have black fur if B is dominant.
Your focus
- Define each of the ten inheritance terms accurately.
- Use the terms correctly in a genetic cross or pedigree.
- Distinguish genotype from phenotype in a worked example.
Genetic inheritance exam tips
Marking Points
- Gamete: a sex cell with a haploid chromosome number, such as sperm or egg.
- Chromosome: a structure of DNA that carries many genes; gene: a DNA section coding for a protein or characteristic.
- Allele: a different form of the same gene; dominant alleles are expressed when one copy is present, recessive alleles only when two copies are present.
- Homozygous: two identical alleles for a gene; heterozygous: two different alleles for a gene.
- Genotype: the alleles an organism carries; phenotype: the observable characteristics resulting from genotype and environment.
Examiner Tips
- 💡Learn each term with a short example, such as Bb for heterozygous.
- 💡When defining a term, include the key idea in one precise sentence rather than a long story.
- 💡Use genetic diagrams to show how genotype leads to phenotype and to practise the vocabulary.
Common Mistakes
- Confusing gene and allele; correct this by saying a gene is a section of DNA and an allele is a version of that gene.
- Using dominant to mean common or stronger; correct this by defining dominant as the allele expressed when one copy is present.
- Treating genotype and phenotype as the same; correct this by stating genotype is the allele combination and phenotype is the observable characteristic.