(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.

(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 Hb^A and Hb^T controls the expression of this disease.
Conditions for thalassemia:

Hb^A and Hb^A: Normal
Hb^A and Hb^T: Carrier

Hb^T and Hb^T: Diseased

Let us assume that both father and mother are the carriers (Hb^A Hb^T) of beta thalassaemia.

Parents		Hb^AHb^T (Father)	x	Hb^AHb^T (Mother)
Offsprings	Hb^AHb^A Normal child	Hb^AHb^T Carrier child with thalassaemia trait	Hb^AHb^T Carrier child with thalassaemia trait	Hb^THb^T 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
X^hY: Haemophilic
X^hX: Carrier
X^hX^h: Haemophilic
Let us assume that a carrier female (X^hX) is married to a normal male.

Parents		XY (Male)	x	X^hX (Female)
Offspring	X^hX Carrier female	XX Normal female	X^hY Haemophilic male	XY Normal male

Parents		XY (Male)	x	X^hX (Female)
Offspring	X^hX Carrier female	XX Normal female	X^hY Haemophilic male	XY Normal male

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A child by the family from Thalassemia is born to a normal couple. But the mother is being blamed by the family for delivering a sick baby. (a) What is Thalassemia?

(b) How would you counsel the family not to blame the mother for delivering a child suffering from this disease? Explain.

(c) List the values your counseling can propagate in the families.

Explain the genetic basis of blood grouping in human population.

(a) Explain a monohybrid cross taking seed coat colour as a trait in Pisum sativum. Work out the cross upto F₂ generation.

(b) State the laws of inheritance that can be derived from such a cross.

(c) How is the phenotypic ratio of F₂ generation different in a dihybrid cross?

What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativum? Workout the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance?

Principles of Inheritance and Variation

(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.

(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.