Patterns of Inheritance (Part 6)

Question 1

Examples of Y-linked inheritance

Answer 1

• Various mutations in the SRY genes
• H-Y histocompatibility antigen
• Hairy ears

Question 2

Variable Expression

Answer 2

• In individuals who have inherited the mutant allele, some individuals are severely affected and others are mildly affected
• Hemochromatosis (autosomal recessive disorder) – more severe in males
• Xeroderma pigmentosum (autosomal recessive) – more severe in individuals exposed more frequently to UV radiation

Question 3

Pleiotropy

Answer 3

A disease causing mutation affects multiple organ systems

e.g.
• Marfan syndrome (autosomal dominant)
-Mutation in the fibrillin gene
-Skeletal abnormalities (long limbs, pectus excavatum)
-Hypermobile joints
-Ocular abnormalities (myopia, lens dislocation)
-Cardiovascular disease (Mitral valve prolapse, Aortic aneurysm)

• Osteogenesis imperfecta (Bone, Sclera) is due to a mutation in collagen gene

Question 4

Locus heterogeneity

Answer 4

Mutations at different loci that cause the same disease phenotype

• Osteogenesis imperfecta: Defect in collagen
– Mutations of chromosome 17 or chromosome 7
– lead to the disease manifestations of osteogenesis imperfecta

• Other disorders that demonstrate locus heterogeneity:
– Sensorineural hearing impairment
– Retinitis pigmentosa
– Charcot Marie Tooth disease