Peggers’ Super Summaries: Basic Sciences Genetics
CHROMOSOMAL STRUCTURE AND FUNCTION
 46 chromosomes
o 22 autosomal pairs
o 2 sex chromosomes
 Contain
o DNA
 4 purine bases
 Adenine-guanin pair (purine bases)
 Cytosine – thymine pair (pyrimidine bases)
 Functions
 Growth and division or mitosis
 Transcription of mRNA
 Protein synthesis
o RNA
polysaccharides
o Histone and non histone proteins
CHROMSOMAL ABNORMALITIES
 Whole chromosomal abnormalities
o Monosomy
 Turner’s syndrome XO
o Trisomy
 Trisomy 21 with extra chromosome causing Down syndrome
 Single gene inheritance
o Autosomal dominant
 Achondroplasia / osteogenesis imperfect
 50% risk of passing on condition
o Autosomal recessive
 Sickel cell
 25% risk of passing on condition
 25% risk of carrier
o X linked dominant
 Hypophosphataemic rickets
o X linked recessive
 haemophilia
Peggers’ Super Summaries: Basic Sciences Genetics
CHROMOSOMAL CONDITIONS
 Achondroplasia
o Short limb dwarfism
o 87% new mutation on chromosome 4
o FGF receptor 3
 Osteogenesis imperfect
o Defect of type 1 collagen
o Osteopenia, bone fragility, blue sclera, ligament laxity
 Duchenne’s
o Dystrophin gene defect
 Marfan Syndrome
o Fibillin gene defect
 X linked rickets
o PEX gene defect
 Hereditory Exostosis
o EXT 1or2 gene defect