List of top Questions asked in CBSE CLASS XII

Read the following passage and answer the questions that follow:

The process of copying genetic information from template strand of DNA into RNA is called transcription. It is mediated by RNA polymerase. Transcription takes place in the nucleus of eukaryotic cells. In transcription, only a segment of DNA and only one of the strands is copied into RNA. 

Read the following passage and answer the questions that follow:

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow : 

The following questions are based on haemophilia.

(i) Work out the crosses between :

(I) Normal female and Haemophilic male

(II) Carrier female and Normal male

(III) Carrier female and Haemophilic male

(ii) Write the conclusions you draw from these crosses. Comment on the type of inheritance of the disease.

(Use : $X$ - Normal, $X^h$ - Haemophilic)

The allele for brown eyes (B) is dominant over blue eyes (b). In a population, 36% of individuals have blue eyes.

Assuming Hardy-Weinberg equilibrium, calculate :

(i) Frequency of allele B

(ii) Percentage of heterozygous individuals

(iii) Percentage of individuals that are homozygous dominant

(Working to be shown)

Study the sequence of bases in a DNA molecule that is shown below and answer the questions.

\( 5^{\prime} - \mathrm{GAATTC} - 3^{\prime} \)
\( 3^{\prime} - \mathrm{CTTAAG} - 5^{\prime} \)

(a) What are such sequences called? Name the enzyme used that recognises such nucleotide sequences.

Study the given chart showing the evolution of plants. Answer the following questions:
(a) Identify the plant which acts as an immediate ancestor of both ferns and conifers.
(b) Name the nearest ancestors of flowering plants.
(c) Name the most primitive group of plants.
(d) Psilophyton provides common ancestry to which classes?
(e) Name the common ancestor of Psilophyton and seed ferns.
(f) Name the common ancestor of mosses and tracheophytes.
What is pedigree analysis? Mention its importance in human genetics. (2 pts.)
Do all pollen grains remain viable for the same length of time? Support your answer with two suitable examples.
Assertion (A) : The population of melanized moths increased in industrial areas after Industrial Revolution.
Reason (R) : In Industrial environment lichen covered trees were replaced by soot-covered trees offering better camouflage to dark coloured moths.

What are sacred groves ? Name any four sacred groves and mention the places where they are found in India.

If a person is having karyotype 47, XXY, name the genetic disorder he is suffering from. Write down symptoms of such a genetic disorder.

(a) Draw a labelled diagram of a human sperm. (Label any four parts)

(b) Define spermiogenesis and spermiation.

Construct a pyramid of biomass starting with Phytoplanktons and label three trophic levels. Is the pyramid upright or inverted ?

Which one of the following fish is being illegally introduced for aquaculture purposes and is posing a threat to the indigenous catfishes in our rivers ?

Which type of interaction is being shown in the figure given below ?



Assertion (A) : Blastocyst becomes embeded in the endometrium of the uterus.

Reason (R) : The morula divides and transforms into blastocyst.

Gambusia is a fish which is being introduced into ponds in order to check vector-borne diseases. Select the option that indicates the correct disease.

Assertion (A) : ELISA is based on the principle of antigen antibody interaction.

Reason (R) : ELISA can detect the proteins/glycoproteins only when present in high concentration.

Endosperm is completely consumed by the developing embryo in which of the following plants ? Choose the correct option.

The human protein which is being obtained from transgenic animals and is used to treat emphysema is :

Biocontrol agents like Dragonflies are used to get rid of which of the following pests/insects ?

Which of the following options correctly depicts the recognition site for EcoRI ?

Identify the disease which is an inborn error of metabolism and is also inherited as the autosomal recessive trait.

Assertion (A) : Endosperm in angiosperm is a triploid tissue.
Reason (R) : Endosperm is formed after triple fusion i.e. fusion, of a diploid secondary nucleus with a haploid male gamete.

(i) Where do the signals for parturition originate from, in humans ?

(ii) Why is it important to feed newborn babies on colostrum ?