Answer the following question.

Question 15 Marks

Sickle cell anaemia: symptoms and treatment.

Answer

Sickle-cell anaemia is a hereditary disease caused due to mutation in a single gene. It is a monogenic disorder.
Normal haemoglobin has glutamic acid as the 6th amino acid in its molecular structure. However, if it is replaced by valine, the shape/structure of the haemoglobin molecule, changes.
Due to this, the erythrocytes (RBCs) which are normally biconcave become sickle-shaped. This condition is called sickle-cell anaemia. The oxygen-carrying capacity of haemoglobin in such individuals is very low.
In this condition, clumping and thereby, destruction of erythrocytes occurs most often. As a result, blood vessels are obstructed and the circulatory system, brain, lungs, kidneys, etc. are damaged.
Symptoms of sickle-cell anaemia are swelling of legs and hands, pain in joints, severe general body aches, frequent cold and cough, constant low-grade fever, exhaustion, pale face, low haemoglobin count.
A person suffering from sickle-cell anaemia should take a tablet of folic acid daily.

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Question 25 Marks

Monogenic disorders

Answer

Disorders occurring due to mutation in any single gene into a defective one are called monogenic disorders.
Approximately 4000 disorders of this type are now known.
Due to abnormal genes, their products are either produced in insufficient quantity or not produced at all.
It causes abnormal metabolism and may lead to death at a tender age.
Examples of monogenic disorders are Hutchinson’s disease, Tay-Sachs disease, galactosaemia, phenylketonuria, sickle cell anaemia, cyctic fibrosis, albinism, haemophilia, night blindness etc.

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Question 35 Marks

Down syndrome

Answer

Down syndrome is the disorder arising due to chromosomal abnormality.
This is the first discovered and described the chromosomal disorder in human beings.
This disorder is characterized by the presence of 47 chromosomes. It is described as the trisomy of the 21st pair.
Infants with this disorder have one extra chromosome with the 21st pair in every cell of the body. Therefore, they have 47 chromosomes instead of 46.
Children suffering from Down syndrome are usually mentally retarded and have a short lifespan. Mental retardation is the most prominent characteristic.
Other symptoms include short height, short wide neck, flat nose, short fingers, scanty hair, single horizontal crease on palm and a life expectancy of about 16-20 years.

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Question 45 Marks

Show the monohybrid cross between (RR) and (rr) and write the phenotypic and genotypic ratio of $F _2$ generation.

Answer

Parental Generation $\left( P _1\right)$

Phenotypic ratio : 3 Round : 1 Wrinkled
Genotypic ratio : 1 RR : 2 Rr : 1 rr

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Question 55 Marks

How do specific traits or characteristics appear in organisms?

Answer

Information necessary for synthesis of a particular protein is stored in the DNA.
The segment of DNA which contains all the information for synthesis of a particular protein is called a gene for that protein.
To understand how a specific trait is expressed, let us consider plant height as an example.
We know that there are growth hormones in plants. Increase in the height of plants depends upon the quantity of growth hormones.
The quantity of growth hormone produced by a plant depends upon the efficiency of the concerned enzyme.
Efficient enzymes produce a greater quantity of the hormone due to which the height of the plant increases.
However, if the enzymes are less efficient, a smaller quantity of hormone is produced leading to the stunting of the plant.
Thus, the expression of traits is controlled by the genes.

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Question 65 Marks

Distinguish between monohybrid and dihybrid cross.

Answer

Monohybrid cross	Dihybrid cross
(i) Cross involving a single pair of contrasting characters is called monohybrid cross.	(i) Cross involving two pairs of contrasting characters is called a dihybrid cross.
(ii) F1 plants of monohybrid cross produce two types of gametes.	(ii) F1 plants of dihybrid cross produce four types of gametes.
(iii) Monohybrid cross has a phenotypic ratio of 3 : 1 in F2 generation.	(iii) Dihybrid cross has a phenotypic ratio of 9 : 3 : 3 : 1 in F2 generation.

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Question 75 Marks

Explain Mendel’s dihybrid ratio with the help of any one cross.

Answer

- In dihybrid cross, Mendel considered two pairs of contrasting characters.
- He made a cross between a pea plant producing rounded and yellow couloured seeds and a pea plant with wrinkled and green coloured seeds.

- All the plants produced in $F_1$_ generation had rounded yellow seeds. This is because in pea plants, round shape of seed is dominant over wrinkled shape and yellow colour of seed is dominant over green colour.
- When $F_1$ plants are self pollinated, they produce four types of gamates – $RY, Ry, rY, ry.$
- $F_2$ plants formed by the fusion of four types of male gametes and four types of female gametes, had phenotypes such as round yellow, wrinkled yellow, round green and wrinkled green.
- Also, $F_2$ generation showed nine different types of genotypes such as $RRYY, RRYy, RRyy, RrYY, RrYy, Rryy, rrYY, rrYy, rryy$.
- Phenotypic ratio of dihybrid cross is

The genotypic ratio of dihybrid cross is

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Question 85 Marks

Explain Mendel’s monohybrid progeny with the help of any one cross.

Answer

Mendel brought about a cross between two pea plants with only pair of contrasting characters. This type of cross is called a monohybrid cross.
Tall pea plants and dwarf pea plants were used in this cross. Hence this is parent generation $(P_1)$.

All the plants produced in $F _1$ genration are tall, having genotype Tt . This indicates that the gene responsible for tallness in pea plants is dominant over the gene responsible for dwarfness.
When $F_1$ plants are self pollinated they produce second filial generation $\left(F_2\right)$.
In $F_2$ generation both tall and dwarf plants appeared in the ratio $3:1.$
Thus, the genotypic ratio of $F _2$ generation is $3$ (Tall) : $1$ (Dwarf) and the genotypic ratio is $1 TT : 2 Tt : 1 tt$.

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Question 95 Marks

Which were the seven pairs of contrasting characteristics studied by Mendel in pea plant?

Answer

The seven pairs of contrasting characters studied by Mendel in pea plant were as follows:

Characters	Dominant	Recessive
Shape of the seed	Round(R)	Wrinkled (r)
Colour of the seed	Yellow (Y)	Green (y)
Colour of the flower	Purple (C)	White (c)
Shape of pod	Inflated (I)	Constricted (i)
Colour of pod	Green (G)	Yellow (g)
Position of flower	Axillary (A)	Terminal (a)
Height of the plant	Tall (T)	Dwarf (t)

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Question 105 Marks

Name some dominant and recessive characteristics seen in human beings.

Answer

Some dominant and recessive characteristics of human beings.

Dominant	Recessive
Rolling tongue	Non-rolling tongue
Presence of hair on arms	Absence of hair on arms
Black and curly hair	Brown and straight hair
Free earlobe	Attached earlobe

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Question 115 Marks

What are the main objectives of National Health Mission?

Answer

The main objectives of National Health Mission are:

Strengthening of the rural and urban health facilities.
Controlling various diseases and illnesses.
Increasing public awareness about health.
Offering financial assistance to patients through various schemes.

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Question 125 Marks

Complete the table for number of chromosomes in different organisms.

Answer

Organism	No. of Chromosomes
Crab	200
Maize	20
Frog	26
Roundworm	04
Potato	48
Human	46
Dog	78
Elephant	56
Fruit fly	08
Mango	40

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Question 135 Marks

What are the effects of tobacco consumption?

Answer

Smoking of cigarettes and bidis adversely affects the process of digestion.
It causes a burning sensation in the throat and cough.
Excessive smoking causes instability and trembling of fingers.
It causes dry cough which leads to sleeplessness.
Tobacco consumption can lead to shortening of life span, chronic bronchitis, pericarditis, cancer of the lungs, mouth, larynx (voice box), pharynx, urinary bladder, lips or tongue.
The nicotine present in tobacco affects the central and peripheral nervous system. Arteries become hard i.e. it causes arteriosclerosis and hypertension.

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