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Principles of Inheritance and Variation

Short Answer Type

101.

(a) Why is human ABO blood group gene considered a good example of multiple alleles?

(b) Work out a cross up to F1 generation only, between a mother with blood group A (Homozygous) and the father with blood group B (Homozygous). Explain the pattern of inheritance exhibited.

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Long Answer Type

102.

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.

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Short Answer Type

103.

A garden pea plant (A) produced inflated yellow pod, and another plant (B) of the same species produced constricted green pods. Identify the dominant traits.

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Long Answer Type

104.

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?

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Short Answer Type

105. Name the event during cell division cycle that results in the gain or loss of chromosome.

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106. How are dominance, co-dominance and incomplete dominance patterns of inheritance different from each other?

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107.

(a) Sickle celled anaemia in humans is a result of point mutation. Explain.

(b) Write the genotypes of both the parents who have produced a sickle celled anaemic offspring.

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108.

How many chromosomes do drones of honeybee possess? Name the type of cell division involved in the production of sperms by them.

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109.

During a monohybrid cross involving a tall pea plant with a dwarf pea plant, the offspring populations were tall and dwarf in equal ratio. Work out a cross to show how is it possible.

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Long Answer Type

110.
(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.