+91-8076753736 support@wiredfaculty.com
logo
logo

Sponsor Area

Principles Of Inheritance And Variation

Question
CBSEENBI12001833
Wired Faculty App

(a) Why are thalassemia and haemophilia categorized as Mendelian disorders ? Write the symptoms of these diseases. Explain their pattern of inheritance in humans.

(b) Write the genotypes of the normal parents producing a haemophilic son.

Solution

(a) Thalassaemia and haemophilia are categorised as Mendelian disorders because they occur by mutation in a single gene. Their mode of inheritance follows the principles of Mendelian genetics. Mendelian disorders can be

  • autosomal dominant (muscular dystrophy)
  • autosomal recessive (thalassaemia)
  • sex linked (haemophilia)

Symptoms of Thalassaemia

  • Thalassaemia minor results only in mild anaemia, characterised by low haemoglobin level.
  • Thalassaemia major is also known as Cooley's anaemia. In this disease, affected infants are normal but as they reach 6 to 9 months of age, they develop severe anaemia, skeletal deformities, jaundice, fatigue, etc.


Symptoms of Haemophilia

  • Person suffering from this disease does not develop a proper blood clotting mechanism.
  • A haemophilic patient suffers from non-stop bleeding even on a simple cut, which may lead to death.

Pattern of Inheritance of Thalassaemia
Pair of alleles HbA and HbT controls the expression of this disease.
Conditions for thalassemia:

  • HbA and HbA: Normal
  • HbA and HbT: Carrier
HbT and HbT: Diseased
Let us assume that both father and mother are the carriers (HbA HbT) of beta thalassaemia.

Parents

 

HbAHbT  
(Father)

x

HbAHbT
(Mother)

Offsprings

HbAHbA
Normal child

HbAHbT 
Carrier child
with thalassaemia trait

HbAHbT 
Carrier child
with thalassaemia trait

HbTHbT
Child with 
severe thalassaemia

Pattern of Inheritance of Haemophilia:
Haemophilia is an X-linked genetic disorder. Compared to females, males have higher chances of getting affected because females have XX chromosomes while males have only one X with Y chromosome. Thus, for a female to get affected by haemophilia, she has to have the mutant gene on both the X chromosomes while males can be affected if they carry it on the single X chromosome.
Conditions for haemophilia:
XY; XX: Normal
XhY: Haemophilic
XhX: Carrier
XhXh: Haemophilic
Let us assume that a carrier female (XhX) is married to a normal male.

Parents

 

XY  
(Male)

x

XhX
(Female)

Offspring

XhX
Carrier
female

XX
Normal
female


XhY
Haemophilic
male
 

XY
Normal
male

Parents

 

XY  
(Male)

x

XhX
(Female)

Offspring

XhX
Carrier
female

XX
Normal
female


XhY
Haemophilic
male
 

XY
Normal
male

Some More Questions From Principles of Inheritance and Variation Chapter

Mention the phenomenon of pleiotropy by giving an example.

Name the plant that shows incomplete dominance in respect of the colour of its flower.

Write the genotypes of man with blood group A.

What is Mendel’s monohybrid phenotypic ratio ?

Write down Mendel’s dihybrid Phenotypic ratio 

Who were the rediscoverers of Mendelism ?

What are the real determinants of what an organism will become ?

What is the unique feature of F1 generation ?

What will be the genetic make up of an organism which suffers from sickle cell anaemia ?

What do the symbols square and circle in a pedigree chart indicate ?

Mock Test Series

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation