List of top Biology Questions asked in CBSE CLASS XII

Specific site at which meiosis II is completed.

Three crosses were carried out in pea plants with respect to flower colour violet/white (V/v) and flower position axial/terminal (A/a). Study in the table the crosses ‘a’, ‘b’ and ‘c’ where parental phenotypes and their $F_1$ progeny phenotypes are given.
Find the genotypes of each of the parental pairs of crosses ‘a’, ‘b’ and ‘c’.

Explain how GM cotton crop is able to resist insect attacks.

Explain the mechanism of switching ‘on’ of the structural genes of lac operon.

“Regulation of lac operon is referred to be negatively regulated.” Justify giving a reason.

Describe the life cycle of Plasmodium from the time it enters the human body till a female Anopheles mosquito bites an infected person.

Mention the two events of Plasmodium life cycle that occur within the female Anopheles body.

A patient is suffering from the infection of the alveoli of lungs and is showing the symptoms of fever, chills, cough, headache, and bluish-colored lips and fingernails. The patient was diagnosed to be suffering from the infection of:

The linking of the antibiotic resistance gene with the plasmid vector of Salmonella typhimurium by Stanley Cohen and Herbert Boyer was made possible by the enzyme:

In an experiment, {E. coli is grown in a medium containing ${}^{14}NH_4Cl$ (${}^{14}N$ is the light isotope of Nitrogen) followed by growing it for six generations in a medium having the heavy isotope of nitrogen (${}^{15}N$). After six generations, their DNA was extracted and subjected to CsCl density gradient centrifugation. Identify the correct density (Light/Hybrid/Heavy) and ratio of the bands of DNA in CsCl density gradient centrifugation:}

The population growth curve applicable for a population of beetles growing in nature under unlimited resource conditions available to them will be:

Which one of the following represents the correct annealing of primers to the DNA to be amplified in the PCR?

Assertion (A): The stirrer facilitates the even mixing of oxygen availability in a bioreactor.
Reason (R): Stirred-tank bioreactors generally have a flat base.}

Assertion (A): Primary transcripts in eukaryotes are subjected to splicing to remove the introns.
Reason (R): Primary transcripts contain both exons and introns, and the introns are non-functional in eukaryotes.}

Assertion (A): The chronic use of alcohol by a person leads to cirrhosis.
Reason (R): Alcohol addiction at times becomes the cause of mental and financial distress to the entire family of the addicted person.}

Amniocentesis is a very useful and important technique, but due to some reason there is a statutory ban on amniocentesis. Justify this statement.

With reference to the set-ups (A, B, and C) given below, of the electrophoretic separation of a mixture of DNA fragments of varied lengths, answer the questions that follow:

In which one of the two Set-ups, A or B, would you see the DNA fragments separated and why?