Makindo Medical Notes

Related Subjects: |DNA replication |DNA structure in Nucleus |Cell Cycle |Mitosis and Meiosis |Ribosomes |Microtubules |Mitochondria |Smooth and Rough Endoplasmic Reticulum

🧬 Genetic Definitions

• Gene: 🧾 A region of DNA that encodes a protein.
• Genome: 🌍 The complete set of genes of an organism, including coding and non-coding DNA sequences.
• Locus: 📍 The specific location of a gene on a chromosome.
• Chromosome: 📦 Self-replicating structures containing DNA. Humans have 23 pairs (22 autosomes + 1 sex pair).
• Alleles: 🔀 Alternative forms of a gene at the same locus; one allele inherited from each parent.
• Haploid: 🎯 A single set of 23 chromosomes (e.g., egg or sperm).
• Codon: 🧩 A 3-base sequence of nucleotides encoding a specific amino acid.
• Karyotype: 🔬 The number and appearance of chromosomes in a nucleus (46 in humans = 44 autosomes + 2 sex chromosomes).
• Autosome: 🚹🚺 Any chromosome other than the sex chromosomes (22 pairs in humans).

Inheritance Pearl: 🟢 Autosomal recessive → usually metabolic disorders (exceptions: inherited ataxias). 🔵 Autosomal dominant → usually structural disorders (exceptions: hyperlipidaemia type II, hypokalaemia periodic paralysis).

🟢 Autosomal Recessive Conditions (Metabolic)

Usually enzymatic or metabolic defects; both alleles must be faulty:

• ⚪ Albinism
• ⚪ Ataxia telangiectasia
• ⚪ Charcot-Marie-Tooth type 4
• ⚪ Hemochromatosis
• ⚪ Cystic fibrosis
• ⚪ Cystinosis
• ⚪ Fanconi anaemia
• ⚪ Familial Mediterranean fever
• ⚪ Homocystinuria
• ⚪ Sickle cell disease
• ⚪ Thalassemia
• ⚪ Phenylketonuria
• ⚪ Refsum’s disease
• ⚪ Lipid storage diseases (Tay-Sachs, Gaucher’s, Niemann-Pick)
• ⚪ Mucopolysaccharidoses (Hurler’s syndrome, etc.)
• ⚪ Retinitis pigmentosa (AR form)
• ⚪ Wilson’s disease

🔵 Autosomal Dominant Conditions (Structural)

Often affect connective tissue, receptors, or structural proteins:

• 🔹 Achondroplasia
• 🔹 Aniridia
• 🔹 Tuberous sclerosis
• 🔹 Charcot-Marie-Tooth types 1 & 2
• 🔹 Myotonic dystrophy
• 🔹 Gilbert’s syndrome
• 🔹 Hyperlipidemia type II
• 🔹 Ehlers-Danlos syndrome
• 🔹 Facioscapulohumeral muscular dystrophy
• 🔹 Familial hypercholesterolemia
• 🔹 Marfan syndrome
• 🔹 Multiple Endocrine Neoplasia (MEN)
• 🔹 Neurofibromatosis 1 & 2
• 🔹 Polycystic kidney disease (ADPKD)
• 🔹 Retinitis pigmentosa (AD form)
• 🔹 Retinoblastoma
• 🔹 Von Willebrand’s disease

🧑‍🍼 X-Linked Recessive Conditions

Affect males (only one X chromosome). Females usually carriers unless they have Turner syndrome (XO).

• ❌ G6PD deficiency
• ❌ Hunter syndrome
• ❌ Hemophilia A & B
• ❌ Fabry disease
• ❌ Duchenne & Becker muscular dystrophy
• ❌ Androgen insensitivity syndrome
• ❌ Color blindness
• ❌ Lesch-Nyhan syndrome
• ❌ Nephrogenic diabetes insipidus
• ❌ Ocular albinism
• ❌ Retinitis pigmentosa (X-linked)
• ❌ Severe combined immunodeficiency
• ❌ Wiskott-Aldrich syndrome

🧬 X-Linked Dominant Conditions

• ⭐ Vitamin D-resistant rickets (more severe in males)
• ⭐ Alport syndrome (85% X-linked dominant)
• ⭐ Rett syndrome