mendelian inheritance

Question 1

Describe the characteristics of Mendelian inheritance, both autosomal and sex-linked.

Answer 1

Autosomal recessive:
-both parents carriers
-50% of offspring is carriers, 25% is affected, 25% is unaffected
e.g. sickle cell anaemia
Autosomal dominant:
- 1 parent affected, 1 unaffected
-50% of affected, 50% unaffected
e.g. huntingtons, achrondroplasia
X-linked:
- gene found on X chromosome
-More prevalent in males as they only have one X chromosome so only need one copy of X chromosome to be affected
- male to male transmission does not occur.
-if father affected and mother unaffected- daughters will all be carriers, sons will be unaffected
-if mother is carrier and father is unaffected- 50% chance of daughter being carrier and 50% chance of son being affected
e.g. Duchenne muscular dystrophy.

Question 2

Give examples of genetic conditions

Answer 2

Autosomal Recessive:
-Sickle cell anaemia: 
abnormal hb gene 
-Cystic fibrosis: 
single gene mutation- 3000 different possible mutations.
symptoms: -sinusitis
-mucus build up in the lungs which can lead to bacterial infection 
-salty sweat in skin glands
-blocked up biliary ducts 
-blocked up pancreatic
 ducts
-complications in reproductive system.
Autosomal dominant:
-Huntingtons 
Sex linked: 
-Duchenne muscular dystrophy: 
-fatal in early life