Inherited Disorders

Inherited Disorders

What Are Inherited Disorders?

Inherited disorders are conditions caused by faulty alleles (mutations) that are passed from parents to offspring through their genes.

💡 Key Concept: These disorders can be dominant or recessive, affecting how likely someone is to inherit the condition.

Key Terms Recap

Term

Meaning

Dominant allele

Only one copy is needed for the disorder to be expressed.

Recessive allele

Two copies are needed for the disorder to be expressed.

Carrier

Someone who has one faulty allele but does not show symptoms.

Examples of Inherited Disorders

1️⃣ Cystic Fibrosis (CF)

Feature

Detail

Cause

Recessive allele (f)

Genotype

Only ff causes the disorder

Symptoms

Thick, sticky mucus in lungs and digestive system

Carriers

People with Ff – no symptoms but can pass it on

👉 Punnett Square Example:
Ff × Ff = 25% FF (healthy), 50% Ff (carrier), 25% ff (has CF)

2️⃣ Polydactyly (extra fingers or toes)

Feature

Detail

Cause

Dominant allele (P)

Genotype

Either PP or Pp has the disorder

Symptoms

Extra fingers or toes

Carriers?

No carriers – if you have the allele, you show the trait

👉 Punnett Square Example:
Pp × pp = 50% Pp (has polydactyly), 50% pp (no disorder)

Embryo Screening

Embryos produced by IVF can be genetically tested for inherited disorders.
✔ Only healthy embryos are implanted into the womb.

Pros

✔ Prevents suffering
✔ Reduces healthcare costs
✔ Allows parents to prepare or avoid passing on the disorder

Cons

❌ Expensive
❌ May lead to ethical issues (e.g. designer babies)
❌ May result in healthy embryos being destroyed

Questions 

  1. What type of allele causes cystic fibrosis?
  2. Can carriers of recessive disorders pass on the condition?
  3. What is the genotype of someone with polydactyly?
  4. What does embryo screening involve?
  5. Name one argument against embryo screening.

Summary 

  • Inherited disorders like cystic fibrosis (recessive) and polydactyly (dominant) are passed through genes.
  • Carriers of recessive disorders do not show symptoms but can pass the gene to children.
  • Embryo screening can be used to avoid passing on serious conditions but raises ethical concerns.