Genetic Disorders — GCSE Biology Revision
Revise Genetic Disorders for GCSE Biology. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to Selective BreedingWhat is Genetic Disorders?
Genetic disorders are conditions caused by abnormalities in an individual's DNA. Some are inherited from parents, caused by faulty alleles, such as cystic fibrosis (a recessive disorder) and polydactyly (a dominant disorder). These can be traced through family trees to predict the probability of inheritance.
Board notes: Covered by all major boards (AQA, Edexcel, OCR). Students should be able to use Punnett squares to predict the inheritance of single-gene disorders like cystic fibrosis and polydactyly.
Step-by-step explanationWorked example
Cystic fibrosis is a recessive disorder. If two parents are both carriers (Cc), there is a 25% chance (1 in 4) of them having a child with cystic fibrosis (cc), a 50% chance of having a carrier child (Cc), and a 25% chance of having an unaffected child (CC). This can be shown with a Punnett square.
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Common mistakes
- 1Assuming all genetic disorders are inherited. While many are, some can arise from spontaneous mutations in the DNA during an individual's lifetime.
- 2Confusing recessive and dominant disorders. For a recessive disorder like cystic fibrosis to be expressed, an individual must inherit two faulty alleles (cc). For a dominant disorder like polydactyly, only one faulty allele (P) is needed.
- 3Thinking that being a 'carrier' means you have the disorder. A carrier is heterozygous for a recessive disorder (e.g., Cc for cystic fibrosis). They do not have the disorder themselves but can pass the faulty allele on to their children.
Genetic Disorders exam questions
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Genetic Disorders
Core concept
Genetic disorders are conditions caused by abnormalities in an individual's DNA. Some are inherited from parents, caused by faulty alleles, such as cystic fibrosis (a recessive disorder) and polydacty…
Frequently asked questions
What is cystic fibrosis?
Cystic fibrosis is an inherited disorder that affects cell membranes, causing the body to produce thick, sticky mucus. This can lead to problems with the lungs and digestive system.
What is embryonic screening?
Embryonic screening is a process where embryos created through IVF are genetically tested for certain disorders before being implanted. It allows parents with a known risk of passing on a genetic disorder to select a healthy embryo.