Patterns of inheritance:
·
Autosomal Dominant
o =Single gene abnormalities expressed in heterozygotes
o M = F, 50% risk of passing it to kids
o 1 abnormal gene causes disease
o Eg Huntington Disease, Marfan Syndrome, Achondroplasia (disturbance of epiphyseal chrondroblastic bone formation)
o But:
§ Variable expression, variable age of onset
§ Non-penetrance happens
§ Gonadal mosaicism (esp if old paternal age) ® somatic
genes normal, mutation in gonads
·
Autosomal Recessive:
o = Only symptomatic when both alleles at a locus on homologous
chromosomes are defective
o Must have mutations in both genes Þ both parent‟s carriers
o Shows up early (no normal genes)
o Eg cystic fibrosis, phenylketonuria
·
X-linked Recessive:
o Only affects males
o Impact early (no normal gene)
o Females are carriers (random X inactivation should mean that 50% of
cells are abnormal. But they‟re usually in the minority. Still may have some
traits)
o Eg haemophilia, Duchenne muscular dystrophy (wasting muscle disease –
most dystrophies are X linked)
·
X-linked Dominant: eg Fragile X
·
Multifactorial:
o Common diseases
o Genetic predisposition plus environmental influence
o Eg Cleft lip/palate
·
Others: mitochondrial, tumour
predisposition
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