AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Some disorders are inherited. These disorders are caused by the…
Full specification wording
Inherited disorders: Some disorders are inherited. These disorders are caused by the inheritance of certain alleles.
An inherited disorder is a condition passed from parents to offspring through alleles in gametes.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 1 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
An inherited disorder is a condition passed from parents to offspring through alleles in gametes. 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.
What earns the marks
- 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.
Common mistakes and how to put them right
Saying that inherited disorders are caught from another person.
Put it right 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.
Put it right by explaining that both parents may be carriers who do not show the disorder.
Confusing a carrier with someone who has the disorder.
Put it right by stating that a carrier has one recessive allele but does not show the characteristic.
Exam 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.
Try the lesson
The start of the Inherited disorders: Some disorders are inherited. These disorders are caused by the inheritance of certain alleles. lesson, made from checked teaching notes for this specification point.
Have a go first
Cystic fibrosis and polydactyly are examples of inherited disorders. What is the fundamental cause of these inherited disorders?
Listen
An inherited disorder is a condition passed from parents to offspring through alleles in gametes. 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. A strong answer earns marks for these 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. A common slip: Saying that inherited disorders are caught from another person. Instead, stating that they are passed through alleles in gametes from parents. Exam tip: Use the terms allele, dominant, recessive and carrier accurately, because these words carry the marks in inheritance questions.
Key words
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Inherited disorder
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Dominant allele
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Recessive allele
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Carrier
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See every definition
- Inherited disorder
- A condition caused by the inheritance of certain alleles passed from parents to offspring in gametes.
- Dominant allele
- An allele that causes a disorder when at least one copy is present, so one copy is enough.
- Recessive allele
- An allele that causes a disorder only when two copies are present.
- Carrier
- A person with one recessive allele who does not show the disorder but can pass the allele on to their children.
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