question_answer

What are biofertilizers? Explain with examples.

OR

(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.

Answer:

Chemical fertilizers like NPK are used in agriculture to increase the fertility of soil and thereby increase the productivity. But the harmful effects of chemical fertilizers have compelled us to look out for an alternative source of fertilizers of biological origin. These fertilizers are called biofertilizers. They also increase the fertility of soil and are economic and ecofriendly. The sources of biofertilizers are bacteria, fungi and cyanobacteria.

(i) Bacteria - Symbiotic nitrogen fixing bacteria Rhizobium leguminosarium lives symbiotically in the root nodules of leguminous plants and fix atmospheric \[{{N}_{2}}\]increasing soil fertility. Free-living \[{{N}_{2}}\] fixing bacteria are Azospirillum and Azotobacter.

(ii) Fungi - Fungi form symbiotic associations with higher plants called mycorrhiza, e.g., Glomus. The fungal partner of this association absorbs phosphorus from soil and passes it to plants. It plays a significant role in phosphate nutrition of plants.

(iii) Cyanobacteria - Free-living nitrogen fixing cyanobacteria are Nostoc, Anabaena, Oscillatoria etc. Azolla-Anabaena symbiotic system is the main biofertilizer used in rice fields. Now a days a large number of biofertilizers are available in the market.

OR

(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 Coolers 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 \[H{{b}^{A}}\]and \[H{{b}^{T}}\]controls the expression of this disease.

Conditions for thalassemia:

\[H{{b}^{A}}\] and \[H{{b}^{A}}\]  :  Normal

\[H{{b}^{A}}\]and \[H{{b}^{T}}\]  :  Carrier

\[H{{b}^{T}}\] and \[H{{b}^{T}}\]  :  Diseased

Let us assume that both father and mother are the carriers \[(H{{b}^{A}}h{{b}^{T}})\]of beta thalassaemia.

 

Parents		\[H{{b}^{A}}\]\[H{{b}^{T}}\] (Father)	\[\times \]	\[H{{b}^{A}}\]\[H{{b}^{T}}\] (Mother)
	\[H{{b}^{A}}\] Normal	Carrier child	Carrier child	Child with
Offsprings	Child	with thalassaemia trait	with thalassaemia trait	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 2X chromosomes while males have only X and Y chromosome. Thus, for a female to get affected by haemophilia, she has to have the mutant allele 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

\[{{X}^{h}}Y\] : Haemophilic

\[{{X}^{h}}X\] : Carrier

\[{{X}^{h}}{{X}^{h}}\] : Haemophilic

Let us assume that a carrier female\[({{X}^{h}}X)\] is married to a normal male.

 

Parents		\[XY\] (Male)	\[\times \]	\[{{X}^{h}}X\] (Female)
Offsprings	\[{{X}^{h}}{{X}^{h}}\]	\[XX\]	\[{{X}^{h}}X\]	\[XX\]
	Carrier	Normal	Haemophilic	Normal
	female	female	male	male

 

(b) When a normal male marries a carrier female (she is considered normal as she contains the mutant gene on one other X chromosomes), they can produce a haemophilic son. So, the genotype of the parents would be XY and \[{{X}^{h}}X\].

 

Parents		\[XY\] (Male)	\[\times \]	\[{{X}^{h}}X\] (Female)
Offsprings	\[{{X}^{h}}X\]	\[XX\]	\[{{X}^{h}}X\]	\[XY\]
	Carrier	Normal	Haemophilia	Normal
	daughter	daughter	son	son