Inherited disorders — AQA GCSE Biology
Test yourself on Inherited disorders with AQA GCSE practice questions.
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Inherited disorders explained
An inherited disorder is a condition passed from parents to offspring through alleles in gametes.
Read the full explanation
It is not caused by infection, diet or lifestyle, although environment can influence how a disorder affects a person. A person inherits one allele of each gene from each parent, so the combination of alleles they receive determines whether they develop the disorder. Some disorders, such as polydactyly, are caused by a dominant allele, so one copy is enough. Others, such as cystic fibrosis, are caused by a recessive allele, so two copies are needed. A carrier has one recessive allele but does not show the disorder and can pass the allele to their children.
Your focus
- Define an inherited disorder as a condition caused by alleles passed from parents.
- Explain how dominant and recessive alleles produce different patterns of inheritance.
- Describe the role of carriers in the inheritance of a recessive disorder.
Inherited disorders exam tips
Marking Points
- State that inherited disorders are caused by alleles passed from parents to offspring in gametes.
- Distinguish inherited causes from environmental or infectious causes of disease.
- Explain that the alleles a person inherits determine whether they develop the disorder.
- Recognise that dominant alleles cause a disorder when at least one copy is present, while recessive alleles cause a disorder only when two copies are present.
- Describe a carrier as a person with one recessive allele who does not show the disorder but can pass the allele on.
- Use family pedigree or genetic cross information to identify how a disorder may have been inherited.
Examiner Tips
- 💡Use the terms allele, dominant, recessive and carrier accurately, because these words carry the marks in inheritance questions.
- 💡When explaining a family history, track alleles through each generation rather than describing only the people who show the disorder.
- 💡Link the cause of the disorder to the alleles inherited, not to the symptoms, so your answer addresses inheritance directly.
Common Mistakes
- Saying that inherited disorders are caught from another person; correct this by stating that they are passed through alleles in gametes from parents.
- Assuming that a person with a recessive disorder must have a parent who also shows the disorder; correct this by explaining that both parents may be carriers who do not show the disorder.
- Confusing a carrier with someone who has the disorder; correct this by stating that a carrier has one recessive allele but does not show the characteristic.