Single gene disorders

• What causes Single gene disorders

  
  

  Point mutations in germline cells.
• Define Sex-linked disorder

  Caused by a gene on the X chromosome
• What are the features of Autosomal recessive inheritence

  • Phenotype apparent only in individuals homozygous for disease allele
  • Heterozygous parents (carriers) unaffected
  • Complete loss of gene function leads to phenotype
• What are the features Autosomal dominant inheritence

  • Phenotype apparent in heterozygotes
  • Partial loss of gene function (haploinsufficiency) leads to phenotype
  • Toxic protein interferes with cell function
• What are the modes of inheritancce for single gene disorders

  Autosomal or sex-linked.
• What are the autosomal modes of inheritance

  Recessive or Dominant.
• what are the two main examples of autosomal recessive conditions

  Sickle cell anaemia and cystic fribrosis.
• What condition is caused by a complete loss of gene function

  Cystic fibrosis
• What are the two main dominant autosomal conditions

  Familial hyperchlosterolaemia and huntington's disease.
• What condition results from haploininsufficiency

  Familial hypercholesterolaemia
• What condition results from a toxic protein interfering with cell function

  Huntington's disease.
• What is haploininsufficiency

  A partial loss of gene function.
• What is heterozygote advantage

  When the carriers of a disease have a form of resistance to another.
• What disease does sickle cell anaemia provide resistance to

  Malaria
• What is the pathology of sickle cell anaemia

  Missense mutation of Amino acid 6 due to a substitution. Misfolding of the Beta chains. Resulting in misshaped red blood cells.
• What are the symptoms of sickle cell anaemia 


  • Anaemia
  • Joint pain
  • Swollen spleen
  • Frequent severe infections
• When do heterosygotes express the SCA phenotype

  At low oxygen environments.
• What is the treatment for SCA

  Regular blood transfusions.
• What is the cure for SCA

  Bone marrow transplant.
• what is huntington's disease

  Late-onset degredation of the brain
• What are the symptoms of Huntington's disease

  • Jerky movements
  • Personality changes
• How does death from huntington's disease arise

  Due to complications such as choking, infection or heart failure.
• What causes huntington's disease

  Defect in the HD gene on chromosome 4. Increased CAG repeats code for glutamine which causes neruon degradation.
• What is the pathology familial hypercholesterolaemia

  Lack of LDL receptors on the liver results in an accumulation of cholesterol in the blood.
• What are the causes of familial hypercholesterolaemia

  Haploininsufficiency. Incomplete dominance as heterozygotes express a mild version of the disease.
• What is the treatment for familial hypercholesterolaemia


  Cholesterol lowering drugs. Low cholesterol diet.
• How does a male recieve a sex-linked condition

  From the mother.
• How does a female recieve a sex-linked condition

  From the father.
• What is duchenne muscular dystrophy

  Muscle waisting disease.
• What causes death in duchenne muscular dystrophy

  Respiratory or cardiac failure.
• What causes duchenne muscular dystrophy

  The affected gene codes for dystrophin which connects muscle fibres to the ECM.