Human Genetics

Question 1

Autosomal Dominant

Answer 1

• An affected person usually has at least one affected parent
• Affects both genders
• Transmitted by both genders
• A child born from an affected x unaffected mating has a 50% chance of being affected
  Example: Huntington’s disease

Question 2

Autosomal Recessive

Answer 2

• An affected person usually has unaffected parents
• Parents of affected person are usually aymptomatic carriers
• Affectes both genders
• After one affected child, each subsequent child has a 25%
  chance of being affected
  Example: Cystic Fibrosis, sickle-cell anemia etc.

Question 3

Sex Linked
(X-linked recessive)

Answer 3

• Affects mainly males
• An affected person usually has unaffected parents
• Mother of affected persons are usually asymptomatic
  carriers and may have male relatives
• Females are rarely affected
• There is no male-to-male transmission but in some cases
  (affected male x carrier female) – it might appear to be the
  case
  Examples: Haemophilia, red-green colour blindness etc

Question 4

Sex Linked
(X-linked dominant)

Answer 4

• Affects both genders but more females
  affected
• Females show more variable phenotype
• The child of an affected female has 50%
  chance of being affected
• For an affected male, none of his son but
  all of his daughters are affected

Question 5

Sex Linked
(Y-linked)

Answer 5

• Affects only males
• All affected male has an affected father
• All son of an affected father are affected
• No daughter (and their children) of an
  affected male will be affected
  Example: Usually diseases linked to Male infertility or male specific phenotypes. But not proven