biology MCQs - 12th class Chapter 06 Mcqs

1

Who first observed chromosomes in 1882 while examining salamander larvae cells?

A

Gregor Mendel

B

Walther Fleming

C

James Watson

D

Karl Correns

2

How many pairs of chromosomes do human cells have?

A

46

B

23

C

80

D

32

3

A chromosome is typically composed of what percentages of DNA and protein?

A

50% DNA, 50% Protein

B

60% DNA, 40% Protein

C

40% DNA, 60% Protein

D

100% DNA

4

A complex of DNA coiled around a core of eight histone proteins is known as a:

A

Chromatid

B

Centromere

C

Supercoil

D

Nucleosome

5

The type of chromatin that remains permanently condensed and whose DNA is never expressed is called:

A

Euchromatin

B

Heterochromatin

C

Metachromatin

D

Prochromatin

6

The chromosomal theory of inheritance was first formulated by whom in 1902?

A

Karl Correns

B

Thomas Hunt Morgan

C

Walter Sutton

D

Frederick Griffith

7

Thomas Hunt Morgan's experiments on sex-linked traits were conducted on which organism?

A

Pea plants

B

Mice

C

Neurospora

D

Drosophila melanogaster

8

In Morgan's experiment, what was the eye color of the F1 generation when a white-eyed male was crossed with a normal red-eyed female?

A

All white-eyed

B

All red-eyed

C

Half red, half white

D

All pink-eyed

9

The first evidence of DNA's hereditary nature was provided by Frederick Griffith's experiments on:

A

Bacteriophages

B

Streptococcus pneumoniae

C

E. coli

D

Fruit flies

10

The process of genetic material transfer from one cell to another, as seen in Griffith's experiment, is called:

A

Transcription

B

Translation

C

Transformation

D

Replication

11

In the Hershey and Chase experiment, what radioactive isotope was used to label the DNA of bacteriophages?

A

35S

B

14C

C

32P

D

15N

12

In the Hershey and Chase experiment, which isotope was used to label the protein coats of the viruses?

A

32P

B

35S

C

15N

D

14N

13

Who discovered DNA in 1869 and initially called it 'nuclein'?

A

P.A. Levene

B

Erwin Chargaff

C

Friedrich Miescher

D

Oswald Avery

14

Which of the following nitrogenous bases is a pyrimidine?

A

Adenine

B

Guanine

C

Cytosine

D

All of the above

15

In RNA, thymine is replaced by which nitrogenous base?

A

Adenine

B

Guanine

C

Cytosine

D

Uracil

16

The covalent bond that links nucleotides together in a long chain is called a:

A

Hydrogen bond

B

Peptide bond

C

Phosphodiester bond

D

Ionic bond

17

According to Chargaff's rules, the amount of adenine in DNA is always equal to the amount of:

A

Guanine

B

Cytosine

C

Uracil

D

Thymine

18

The double helical structure of DNA was proposed by Watson and Crick in which year?

A

1944

B

1953

C

1958

D

1969

19

In the DNA double helix, how many hydrogen bonds are formed between guanine and cytosine?

A

One

B

Two

C

Three

D

Four

20

What is the diameter of the DNA double helix molecule?

A

2 nm

B

3.4 nm

C

0.34 nm

D

10 nm

21

The model of DNA replication confirmed by the Meselson-Stahl experiment is:

A

Conservative

B

Dispersive

C

Semi-conservative

D

Liberal

22

In the Meselson-Stahl experiment, what heavy isotope was used to label the bacterial DNA?

A

14N

B

32P

C

35S

D

15N

23

The enzyme that constructs a short RNA primer to initiate DNA synthesis is called:

A

DNA Polymerase III

B

Helicase

C

Ligase

D

Primase

24

Short segments of DNA synthesized on the lagging strand are known as:

A

Telomeres

B

Okazaki fragments

C

Introns

D

Exons

25

Which enzyme joins the Okazaki fragments together?

A

Helicase

B

Primase

C

DNA ligase

D

RNA polymerase

26

DNA replication always proceeds in which direction on the growing strand?

A

3' -> 5'

B

5' -> 3'

C

From the centromere outwards

D

In both directions simultaneously

27

The 'one-gene/one-enzyme' hypothesis was proposed based on experiments with which organism?

A

Drosophila

B

E. coli

C

Neurospora

D

Mice

28

Who were the scientists that proposed the 'one-gene/one-enzyme' hypothesis?

A

Watson and Crick

B

Hershey and Chase

C

Beadle and Tatum

D

Meselson and Stahl

29

Sickle cell anemia is caused by a change from glutamic acid to which other amino acid?

A

Leucine

B

Proline

C

Valine

D

Histidine

30

The process of synthesizing RNA from a DNA template is called:

A

Translation

B

Replication

C

Transformation

D

Transcription

31

The process of synthesizing a polypeptide from an mRNA sequence is called:

A

Transcription

B

Translation

C

Replication

D

Conjugation

32

Which type of RNA transports amino acids to the ribosome?

A

mRNA

B

rRNA

C

tRNA

D

snRNA

33

In prokaryotes, the promoter sequence located at the -10 position is typically:

A

TTGACA

B

TATAAT

C

AUG

D

GC hairpin

34

The subunit of RNA polymerase responsible for correct initiation of transcription is the:

A

Alpha factor

B

Beta factor

C

Omega factor

D

Sigma factor

35

The genetic code is a combination of how many nucleotides per codon?

A

2

B

3

C

4

D

5

36

Which of the following is the standard initiation codon?

A

UAA

B

UGA

C

AUG

D

UAG

37

Which amino acid is encoded by the initiation codon AUG?

A

Leucine

B

Valine

C

Proline

D

Methionine

38

Codons like UAA, UAG, and UGA that do not code for any amino acid are called:

A

Initiation codons

B

Anticodons

C

Nonsense codons

D

Sense codons

39

The genetic code is considered universal, but exceptions are found in the DNA of which organelle?

A

Nucleus

B

Ribosome

C

Mitochondria

D

Chloroplast

40

The enzyme that attaches a specific amino acid to a tRNA molecule is called:

A

RNA polymerase

B

Peptidyl transferase

C

Aminoacyl-tRNA synthetase

D

DNA ligase

41

During translation in prokaryotes, the first tRNA binds to which site on the ribosome?

A

A site

B

P site

C

E site

D

Promoter site

42

A change in the DNA sequence is known as a:

A

Translation

B

Transcription

C

Mutation

D

Allele

43

Down's syndrome is an example of what type of mutation?

A

Point mutation

B

Chromosomal aberration

C

Frameshift mutation

D

Silent mutation

44

Phenylketonuria is caused by a defective enzyme called:

A

Homogentisic acid oxidase

B

Phenylalanine hydroxylase

C

Tyrosinase

D

Hexosaminidase A

45

A typical human chromosome contains about how many nucleotides in its DNA?

A

1.4 million

B

14 million

C

140 million

D

1.4 billion

46

The particular array of chromosomes that an individual possesses is called its:

A

Genotype

B

Phenotype

C

Karyotype

D

Allele set

47

Chromosomes that are V-shaped because the centromere is in the middle are called:

A

Telocentric

B

Acrocentric

C

Sub-metacentric

D

Metacentric

48

The sugar found in DNA is:

A

Ribose

B

Deoxyribose

C

Glucose

D

Fructose

49

In eukaryotes, eukaryotic mRNA is protected from nucleases by a cap and a:

A

Poly-G tail

B

Poly-C tail

C

Poly-A tail

D

Methyl group

50

The enzyme responsible for unwinding the DNA helix during replication is:

A

Ligase

B

Polymerase

C

Primase

D

Helicase