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 intervening DNA sequences.
• Locus: The specific location of a gene on a chromosome.
• Chromosome: Self-replicating genetic structure in cells containing DNA; holds a linear sequence of genes. Typically found in pairs; humans have 23 pairs (22 autosomes + 1 sex chromosome).
• Alleles: Alternative forms of a gene at the same locus on a chromosome; each parent contributes one allele per locus.
• Haploid: A single set of chromosomes (half the full set), present in gametes (egg or sperm), containing 23 chromosomes.
• Codon: A sequence of three nucleotides encoding a specific amino acid.
• Karyotype: The number and appearance of chromosomes in the nucleus; humans have 44 autosomes + 2 sex chromosomes.
• Autosome: Any chromosome other than the sex chromosomes; humans have 22 pairs of autosomes.

Genetic Inheritance Patterns: Autosomal recessive conditions are typically metabolic (exceptions: inherited ataxias). Autosomal dominant conditions are generally structural (exceptions: hyperlipidemia type II, hypokalemic periodic paralysis).

Autosomal Recessive Conditions (Metabolic)

These are usually metabolic disorders, except for inherited ataxias:

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

Autosomal Dominant Conditions (Structural)

Typically structural conditions, except for Gilbert's syndrome and familial hypercholesterolemia:

• Achondroplasia
• Aniridia
• Tuberous sclerosis
• Charcot-Marie Tooth 1 & 2
• Myotonic dystrophy
• Gilbert's syndrome
• Hyperlipidemia Type 2
• Ehlers-Danlos syndrome
• Facioscapulohumeral muscular dystrophy
• Familial hypercholesterolemia
• Marfan syndrome
• Multiple Endocrine Neoplasia (MEN) syndromes
• Neurofibromatosis 1 and 2
• Polycystic kidney disease
• Retinitis pigmentosa (autosomal dominant)
• Retinoblastoma
• Von Willebrand's disease

X-Linked Recessive Conditions

These conditions typically affect males due to the single X chromosome; females are affected if they have Turner syndrome (only one X chromosome).

• G6PD deficiency
• Hunter syndrome (a type of mucopolysaccharidosis; primarily affects males)
• Hemophilia A and B
• Fabry disease
• Becker and Duchenne muscular dystrophy
• Androgen insensitivity syndrome
• Color blindness
• Lesch-Nyhan syndrome
• Nephrogenic diabetes insipidus
• Ocular albinism
• Retinitis pigmentosa
• Severe combined immunodeficiency
• Wiskott-Aldrich syndrome

X-Linked Dominant Conditions

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