Understanding Inherited Disorders Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Explore how genetic disorders are passed from parents to offspring, including the difference between dominant and recessive inheritance patterns using p...

• Explain how inherited disorders are caused by the inheritance of certain alleles
• Compare the inheritance patterns of dominant and recessive disorders using examples
• Calculate the probability of inheriting genetic disorders using genetic crosses
• Evaluate the genetic risks for families with inherited disorders

Key ideas to keep in view

Use this lesson to stay inside B5.1 Inheritance while connecting the detail back to the wider B5: Genes, inheritance and selection topic.

• B5: Genes, inheritance and selection
• B5.1 Inheritance
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Understanding Inherited Disorders before testing yourself from memory.

• Some medical conditions run in families. A child might have the same disorder as their parent or grandparent, even though they've never been exposed to the same environment or lifestyle. These are inherited disorders — conditions written into our DNA.
• A medical condition caused by faulty genes passed from parents to offspring through alleles. The disorder appears because specific alleles are inherited that cause problems with how the body develops or functions.
• Think of your DNA as an instruction manual for building and running your body. Sometimes, there are 'typos' in these instructions — faulty alleles. When these faulty alleles are passed from parent to child, they can cause inherited disorders.
• Trap: Many students think all diseases are inherited. Actually, most diseases are caused by lifestyle, environment, or infections — not genetics. Only disorders caused by faulty alleles count as inherited disorders.
• Not all inherited disorders work the same way. The key difference is whether the faulty allele is dominant or recessive. This determines how likely you are to actually develop the disorder.
• An inherited disorder caused by a dominant allele. You only need one copy of the faulty allele to develop the disorder. If either parent has the disorder, there's a 50% chance each child will inherit it.
• An inherited disorder caused by a recessive allele. You need two copies of the faulty allele to develop the disorder. Both parents must be carriers for a child to potentially inherit the disorder.
• Picture this: dominant alleles are like loud voices in a crowd — even one copy gets heard. Recessive alleles are like whispers — you need two copies speaking together to be heard over the normal allele.
• Polydactyly is a perfect example of how dominant disorders work. People with this condition are born with extra fingers or toes — usually six instead of five.
• An inherited disorder causing extra fingers or toes, caused by a dominant allele. The extra digits can appear on hands, feet, or both. The condition varies from small skin tags to fully formed extra digits.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.