Q.1     In a double stranded DNA has 20% of cytosine, calculate the percentage of adenine in the DNA.

(C=G , i.e. 20%, C+G =40% ,A+T=60% ,A=30%, C=cytosine , T =thymine , G = guanine, A = adenine.)

Q.2.    Depending upon the chemical nature of template (DNA or RNA) and the nature of nucleic acid synthesized from it (DNA and RNA).

(1- DNA dependent DNA polymerase uses a DNA for synthesis of DNA.

2- DNA dependent RNA polymerase uses a DNA template for synthesis of

RNA.

3- RNA dependent DNA polymerase uses a RNA template for the

Synthesis of  DNA ,reverse transcription         .

Q .3.   What do you mean by satellite DNA?

(This DNA represents highly repetitive nature of small stretches of DNA

having distinctive base composition.)

Q.4.    In the medium where E. coli was growing, Lactose was added , which

induced lac operon . But why does lac operon shut down after some time

after addition of lactose in the medium.

(Lactose acct as an inducer , if lactose is present it inactivate the repressor, and induce transcription for beta galactosidase,this enzyme act on lactose and used. If lactose is absent , repressor will bind with operator and stop transcription . In this way the lac operon is shut down.)

Q.5     Which property of the DNA double helix led Watson and Crick to hypothesize semiconservative mode of DNA replication, Explain.

(Forming a new complementary strand or comlementarity)

Q.6.    Define polymorphism.

( If an inheritable mutation is obserbed in a population at high frequency, it is called DNA polymorphism.)

Q.7.    When and at what end does the tailing of the hn RNA take place ?

(After the process of splicing the hn RNA undergoes capping andtailing . In tailing, adenylated residues (2000- 300) are added at 3^, end.)

Q.8.    Name the enzyme involved in discontinuous replication of DNA strand. Mention the polarity of the template strand .

(A separate RNA primer is formed for the synthesis of discontinuous or okazaki strand later it will join together by DNA ligase. The polarity of the template strand will be 3^,-5^,.

Q.9.    Write the sequence of bases through which AUG is transcribed from and its anticodon.

(The sequence of bases through which AUG is transcribed from – TAC, the sequence of bases in its anticodon is UAC.)

Q.10. One of the codon on m RNA is AUG. Draw the structure of t RNA adaptor mole. for this codon.

Q.11. Study the m RNA segment given below which is completed tobe translate into a polypeptide chain.

a UAC     GAG    AGA    UUU       b

I  I  I        I  I  I       I  I  I       I  I  I   I  I   I    I  I  I

Write the codon a and b .

(initiator  AUG and terminator codon UUA)

Q.12. In a eukaryotic cell DNA molecule are organized within the nucleus. How is the DNA molecule organized in a bacterial cell in absence of a nucleus.

(In a bacterial cell DNA molecule is held with some protein in the region of nucleoid. The DNA  in the nucleoid.The DNA in the nucleoid is organized in large loops held by proteins)

Q.13   A polypeptide of 600 amino acid will be coded for by a linear sequence of how many basees in  (a) m RNA  (b)  DNA

(a) 1800  (b) 1800

Q.14. What do you mean by Proof reading in DNA synthesis.

( Replace the wrong bases  added during replication to DNA with correct ones by cooperation of nucleases, DNA polymerases and ligase enzymes.)

Q.15. What do you call a non intervening nucleotide sequence in a eukaryotic gene.

(introns)

Q.16. Name two sulphur containing and two basic amino acids.

( Sulphur containing- Methionine, Cysteine, Basic aminoacid- Lysine and Arginine)

Q.17. Give the site and time of occurrence of transcription.

( Transcription occurs in the nucleus during G₁ and G₂ phase of cell cycle in eukaryotes and in cytoplasm in prokaryotes.)

Q.18. If the sequence of coding strand in a transcription unit is written as follows

5^, - ATGCCTAGGTCCAGGCAT – 3^,

(i) Write down the sequence of m RNA.

(ii) Write down the anticodon for each and their corresponding amino acids.

(  (i)    The template strand for this sequence will be

5,- ATGCCTAGGTCCAGGCAT – 3,  Coding strand

3, – TACGGATCCAGGTCCGTA – 5,  Template strand

(ii) Anticodon codon sequence

5^, - A UGCCUAGGUCCAGGCAU – 3^, m RNA

UAC    GGA   UCC    AGG    UCC     GUA  anticodon

Methionine    proline    arginine   serine      arginine        histidine

Q.19. What do you understand by 5, – end and 3, – end.

(A polynucleotide chain comprise of a long chain of nucleotides

Joined by 3^,- 5^, phosphodiester linkages. Such a polymer has at one

end free phosphate moiety at 5, end of ribose sugar. This end of

Polymer is referred to as 5, end. Similarly at the other end of the

polymer the pentose sugar has a free 3, OH group . This end of

polymer is referred to as 3, end.)

Q.20. Name the amino acids which have only one codon each.

(Methinoine and tryptophan)

Q.21. Is there any base triplet that codes for more than one amino acids.

(no)

Q.22. Name the enzyme that can break and reseal the DNA strand.

(Topoisomerases in eukaryotes and gyrases in eukaryotes.)

Q.23. In human genome which one of the chromosomes has the most genes and which has fewest.

(Chromosomes I^st has the most genes 2968 and

Y chromosomes has the fewest 231 )

Q.24. which enzyme cannot initiate the synthesis of DNA although it can

Catalyze the growth of a DNA chain.

(DNA, polymerase)

Q.25. How does DNA express its biological information?

( By transcribing mRNA and synthesing protein)

HOTS 2012 (QUICK REVISE) Class – XII

Subject – Biology

Topic – Principles of inheritance

1. Which extra chromosomes causes Klineflter Syndrome?

(Sex chromosome , X)

2. The human male never passes on the genes for Haemophilia to his son Why?

(Male sex is determined by Y chromosome which does not bear the genes for Haemophilia)

3. In which two ways numerical changes occur in the chromosomes?

(Aneuploidy and polyploidy)

4. Define linked genes?

(Linked genes are those genes which stay together in heredity transmission and located on the same chromosome.)

5. In sickle cell anemia  glutamic acid is replaced by valine. Write name of triplet code for valine?

(GUG)

6. If a genetic disease is transferred from a phenotypically normal but carrier femaleto only some of the male progeny. The disease will be autosomal dominant or sex linked recessive?

(Sex linked recessive)

7. Condition 2n+1, 2n-1, and 2n+2,2n-2are called aneuploidy or polyploidy?

(Aneuploidy)

8. Mention the condition of karyotype when it will be present in nullisomic and monosomic condition?

(nullisomic,2n-2,and monosomic ,2n-1)

9. What is the cause of sex linked recessive trait, colourblindness?

(X linked recessive gene by causing lack of the primary cone pigment of the retina.)

10. Palm is broad with characteristic crease,this is the symptom of which kind of chromosomal disorder?

(Down syndrome)

11. Failure of cytokinesis after telophase stage of the cell division result in an organism, this is a characteristic  of polyploidy or aneuploidy?                               (polyploidy)

12. Define the term Gynaecomastia?

(Feminine development in Klineflter syndrome)

13. Can disease expressed if the genotype is Hb^A Hb^S for Haemophilia?

(No)

14. Write the name of inborn error of the metabolism and inherited as autosomal recessive trait?

(Phenylketonuria)

15. Write the name of the category of animals in which sex chromosomes are designated as Z and W chromosomes?

(Birds)

16. What other term can be used to replace the term recombination?

(Non parental gene combination)

17. If the frequency of parental forms is higher than 25% in a dihybrid cross , What does that indicate about the two genes involved?

(Homozygous condition)

18. Write the possibility of the genotype of a person with blood group B?

( I^BI^B, I^B i)

19. Name the phenomenon that occur when homologous chromosomes do not separate during meiosis?

(Non disjunction)

20. Even if a character shows multiple allelism , an individual will only have allele for that character. Why?

( Two forms of allele – one from one parent and other from other parent.)