Saturday, January 2, 2021

Principles of Inheritance and Variation | Class 12 Zoology | Previous Years Questions and Answers (2018 to 2020)

 3. PRINCIPLES OF INHERITANCE AND VARIATION


2020 SAY

1.     Select a female heterogametic animal from the following: (1)

(a)    Human beings                 (b)  Drosophila

(c)    Birds                                (d)  Grasshopper

ü Answer:

(c) Birds

2.     Complete the table using appropriate terms: (2)

Klinefelter’s syndrome

(a)

Sterile male

(b)

44A + XO

(c)

(d)

Trisomy 21

Mental retardation

ü Answer:

(a) 44A + XXY

(b) Turner’s syndrome

(c) Sterile female/ ovaries are rudimentary etc.

(d) Down’s syndrome

3.   In a cross between a true breeding red flowered and a true breeding white flowered plants, the F1 generation was pink coloured flowers. From this cross

(a)    Identify the Inheritance.

(b)   Give an example for this type of Inheritance.

(c)    Write the F2 phenotypic and genotypic ratio. (2)

ü Answer:

(a) Incomplete dominance

(b) Flower colour in Snap dragon

(c) Phenotypic ratio = 1:2:1

Genotypic ratio = 1:2:1.


2020 MARCH

1.  From the following, find out the symbol used in the human pedigree analysis representing male. (1)

ü Answer:

(c) ¨

2.  Observe the figure given below showing Mendel's experiment using pea plants. (2)


a.   Identify the cross.

b.  Which are the laws proposed by Mendel based on these observations?

ü Answer:

(a) Monohybrid cross

(b) Law of Dominance, Law of Segregation.

3.   Correct the following statements, if there is any mistake: (2)

a.  Haemophilia is an autosome linked recessive disease.

b.  Turner's syndrome is due to the presence of an additional copy of X chromosome.

ü Answer:

(a) Haemophilia is a sex-linked recessive disease.

Or

Sickle cell anaemia is an autosome linked recessive disease.

(b) Turner's syndrome is due to the absence of an X chromosome

Or

Klinefelter’s syndrome is due to the presence of an additional copy of an X chromosome.

2019 SAY June

1.  Identify the following symbols in pedigree Analysis. (1)

ü Answer:

(a) Mating     (b) Mating between relatives

2.   Observe the cross of a pure violet and white flower. (2)

a.   By using the F1 progeny design a test cross.

b.   Mention the significance of test cross.

ü Answer:

(a)

(b) It is used to find out the unknown genotype of a character.

3.   Each symptom of two chromosomal disorders are given below: (2)

·   Gynaecomastia

·   Rudimentary ovary and lack of secondary sexual characters

a.  Identify the disorders.

b.  Give the reason for these disorders.


ü Answer:

(a) Gynaecomastia: Klinefelter’s syndrome.

Rudimentary ovary and lack of secondary sexual characters: Turner’s syndrome.

(b) Klinefelter’s syndrome: Presence of an additional copy of X-chromosome in male.

Turner’s syndrome: Absence of one X chromosome in female

2019 MARCH


1.   "The sex of the baby is determined by the father and not by the mother." Do you agree with this statement ? Substantiate your answer. (2)


ü Answer:


Yes. Because male can produce two types of gametes (sperms) – one with X chromosome and other with Y chromosome. Y chromosome is responsible for the male sex of the baby. Female can produce only gametes (Egg) containing X chromosome. X chromosome is responsible for female sex of the baby.


2.   Find the odd one out. Justify your answer. (2)


Down's syndrome, Turner's syndrome, Phenylketonuria, Klinefelter's syndrome.


ü Answer:


Phenylketonuria. Because it is a Mendelian disorder. Others are chromosomal disorders.


3.   The amino acid composition of the relevant portion of chain of two haemoglobin molecules (A & B) are shown below. (3)


a.   Which one of the polypeptide chain is abnormal?

b.   Name the disorder caused by it.

c.   What is the reason for this abnormality?

d.   What is the effect of this abnormality in such individuals?


ü Answer:

(a) Chain B.

(b) Sickle cell anaemia.

(c) This is due to the single base substitution at the sixth codon of the β-globin gene from GAG to GUG.

(d) The mutant Hb molecule undergoes polymerization under low oxygen tension causing the change in shape of the RBC from biconcave disc to elongated sickle like structure.


2018 SAY


1.   Observe the following cross between heterozygous dominant progeny and homozygous recessive parent. Answer the following questions. (2)


a.  Identify the cross.

b.  Mention the significance of this cross.


ü Answer:

(a) Test cross.

(b) It is used to find out the unknown genotype of a character.


2.   Following diagram shows amino acid sequences of a part of b-chain of Haemoglobin of two individuals. Observe the amino acid sequence and answer the following questions: (2)


a.  Which among the above indicates sickle cell anaemic condition?

b.  Justify your answer.

c.  Describe what is single base substitution.


ü Answer:


(a) The second b-chain.

(b) In the sixth position, glutamic acid replaced by valine.

(c) Substitution of a single base in the sixth codon GAG to GUG.


3.   The blood group of a child is ‘O’. His father is with 'A' blood group and mother with 'B' blood group. Write down the genotype of the child and genotypes of parents. (2)


ü Answer:


Genotype of the child: ii (O group is always ii).

Genotype of the father: IAi

Genotype of the mother: IBi


2018 MARCH


1.   ln a classroom discussion, a student said that the sex of the baby is determined by father. Analyse the statement and give reason for it. (2)


ü Answer:


This statement is true. Because male can produce two types of gametes (sperms) – one with X chromosome and other with Y chromosome. Y chromosome is responsible for the male sex of the baby. Female can produce only gametes (Egg) containing X chromosome. X chromosome is responsible for female sex of the baby.

2.   

   

       (a) Observe the above cross and name the phenomenon.

(b) Write down the theoretically given explanations of the phenomenon. (2)


ü Answer:


(a) Incomplete dominance.

(b) It is an inheritance in which heterozygous offspring shows intermediate character b/w two parental characteristics.


3.   Hemophilia, Sickle cell anemia and Phenyl Ketonuria are Mendelian disorders. (3)

(a) What do you mean by Mendelian disorder?

(b) Which one of the above is an example of inborn error of metabolism? Mention the cause of the disorder.


ü Answer:


(a) Mendelian disorders are the disorders caused by the alteration or mutation in the single gene.

(b) Phenyl Ketonuria. It is due to mutation of a gene that codes for the enzyme phenyl alanine hydroxylase. As a result, phenylalanine accumulates and converts into phenyl pyruvic acid and other derivatives

 


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