Diagram to show pattern of genetic inheritance for autosomal recessive disorders such as sickle cell disease, cystic fibrosis and thalassaemia

The Parents

Fertilisation

Altered gene only

Normal gene only

Altered gene and normal gene

Altered gene and normal gene

Child has a disorder

(1 in 4 chance in each and every pregnancy)

Child is not affected

(1 in 4 chance in each and every pregnancy)

Child is a carrier

Child is a carrier

(2 in 4 chance in each and every pregnancy)

Carrier father

Altered gene

Normal gene

Carrier mother

Altered gene

Normal gene

Serious risk refer couple for counselling, pre-nataldiagnosis to be offered

Less serious risk refer couple for counselling, further investigationmaybe required

No risk no furtheraction required

Table showing parental carrier state combinations that give rise to the risk of a fetus with significant sickle cell disease or -thalassaemia

Hb S

-thal

d-thal

Hb Lepore

Hb E

Hb OArab

Hb C

Hb DPunjab

HPFH

Not a carrier

Hb

S

-t

hal

d-t

hal

Hb

Lep

ore

Hb

E

Hb

OA

rab

Hb

C

Hb

DPu

nja

b

HPF

H

No

t a

carr

ier

Carrier of:

Table based on the work of Prof. B. Modell.