Question

give an briefly explain 3 forms of inheritance, give an example of each?

Answer 1

Patterns of Inheritance

There are 3 types of inheritance
1)Dominant
2) Recessive
3) Co dominance

1 A)Autosomal Dominant
*.Even in heterozyous state have sufficient amount of expression.
*50 %of progeny is affected .
*Each affected person has an affected parent

*Occurs in every generation
*2 types of mutation are present - Gain of function or loss of function
*It is characterised by incomplete penetrance and variable expressivity .
*Classicically involved with structural proteins
Eg D Dystrophia myotonica
   O. Osteogenesis imperfecta
   M. Marfan syndrome,Multiple endocrine neoplasia
I.     Intermittent porphyria
   N. Neurofibromatosis 1 and 2
   T.     Tuberous sclerosis

1 B)Autosomal Recessive

*Autosomal disorders expresses in homozyous state early onset of presentation of disease .

*It is characterised by involvement of enzymes and most of disorders with enzymatic problems eg Inborn errors of metabolism have this type of inheritance

*Complete penetrance is seen

*Parents are carrier and if both the parents with carrier with each other then there are chances of autosomal recessive .
*Seen in consanguinous marriage ( marriage between relatives )

*Not typically seen in every generation.
Eg Sickle cell disease
Thalassemia
Freidrich Ataxia
Wilson disease
Harmochromatosis
Alkaptonuria
Inborn errors of metabolism -- Glycogen storage and lyosomal storage disorder .

2 A)X-linked Dominant

*Females more frequently affected

*Can have affected males and females in same generation.

*.Affected father transmit the disorder to females Involves structural proteins .

Eg Vitamin D resistant rickets
Incontenti pigmenti

ALPORT SYNDROME
Hereditary spherocytosis
Hungtington disease

2 B)X-linked Recessive

*.Most common form of sex linked transmission

*Males more frequently affected

*Affected males often present in each generation.

Ex Lesch Nyhan syndrome
Haemophilia A and B
Colour blindness
G 6 P D deficiency
Duchenne muscular dystroohy
Fragile X syndrome
Wisckot aldrich syndrome

3) Codominance pattern

*When two alleles for a trait are equally expressed with neither being recessive or dominant, it creates codominance.

Examples of codominance include a person with type AB blood, which means that both the A allele and the B allele are equally expressed.Hence both group of Antigen A and B are present on RBC and from AB blood group of ABO system .