Autosomal Dominant Inheritance

Question 1

Types of Mendelian Inheritance

Answer 1

• Autosomal Recessive
• Autosomal Dominant
• X-linked Dominant
• X-linked Recessive
• Y-linked

Question 2

What are features of Dominant Diseases?

Answer 2

• Heterozygotes express the abnormal phenotype
• Every affected individual has at least one affected parent (except in traits with high mutation rates)
• Since most affected individuals are heterozygous:
  
  • Two affected parents could have an unaffected child
  • Heterozygous individuals with a homozygous recessive (unaffected) spouse have a 50% chance of having an affected child
• the heterozygous phenotype is typically less severe than the homozygous dominant phenotype

Question 3

What are the three types of dominance and how do they differ from one another?

Answer 3

• Simple dominance: 1 allele dominates all other alleles → that one allele expresses the phenotype e.g. ability to roll the tongue.
• Co-Dominance: 2 alleles both dominant → both alleles express in the phenotype when present e.g. ABO blood groups
• Incomplete Dominance: When 2 alleles are present but neither express in the phenotype of a heterozygote i.e. the phenotype is halfway between the two.

Question 4

What are the types of alleles in blood groups?

Answer 4

• 2 dominant alleles (A & B); 1 recessive allele (O).

Question 5

What is Marfan Syndrome?

Answer 5

Genetics and phenotype

• Mutations in the fibrillin gene (FBN1) (tyrosine to STOP codon) on chromosome 15 cause defective and weakened connective tissue

• Multi system disorder with diagnostic criteria being aortic root aneurysm and lens dislocation. [2]
3 | Dr Fiona Ballard

• Affects the skeletal system, cardiovascular system, heart, and eyes.
Individuals are tall and thin, with long arms and legs and thin fingers.

• Weakened connective tissue at the base of the aorta causes it to enlarge and rupture.

Question 6

What is Huntington Disease?

Answer 6

Neurodegenerative behavioural disorder.
Degenerative disease of basal ganglia and cerebral cortex from expansion of a repeating codon on chromosome 4.
Loss of mental function, jerky movements, loss of
neurotransmitter receptors.