List of top Questions asked in CBSE CLASS XII

Using a Punnett square, work out the distribution of an autosomal phenotypic feature in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.
How does the process of Natural Selection affect Hardy-Weinberg equilibrium? Explain with the help of graphs.
Write the composition of intine and exine layers of a pollen grain.
A bilobed dithecous anther has 200 microspore mother cells per microsporangium. How many male gametophytes can be produced by this anther?
Explain how the intake of oral contraceptive pills prevent pregnancy in humans.
List two reasons that make copper releasing IUDs as effective contraceptives.
State the conclusions derived by David Tilman’s long-term ecosystem experiments using outdoor plots.
State the advantage of using thermostable DNA polymerase.
Write the scientific name of the source organism of the thermostable DNA polymerase used in PCR.
The symptoms of malaria do not appear immediately after the entry of sporozoites into the human body when bitten by female Anopheles mosquito. Explain why it happens.
Describe any two situations where a medical doctor would recommend injection of pre-formed antibodies (antitoxins) into the body of a patient.

Study the given pedigree chart in which neither of the parents shows the trait but the trait is present in both male and female children.

pedigree chart

Give one example of such a trait in human beings.

Study the given pedigree chart in which neither of the parents shows the trait but the trait is present in both male and female children.

pedigree chart

Write about the trait, also explain the inheritance of such a trait in the progeny on the basis of the given pedigree chart.

Mention any four strategies adopted by flowering plants to prevent self-pollination.
(A) Comment upon the mode of pollination in Vallisneria and Zostera. (B)
Assertion (A): Restriction endonuclease recognises palindromic sequence in DNA and cuts them. Reason (R): Palindromic sequence has two unique recognition sites PstI and PvuI recognised by restriction endonuclease.

Assertion (A): Streptococcus pneumoniae and \(\textit{Haemophilus influenzae}\) are responsible for causing infectious disease in human beings. 
Reason (R): A healthy person acquires the infection by inhaling the aerosols released by an infected person.

Assertion (A): The number of white winged moths decreased after industrialisation in England. Reason (R): Effects of industrialisation were more marked in rural areas of England.
Assertion (A): Corpus luteum secretes the hormone, progesterone. Reason (R): Hormone Progesterone is essential for maintenance of the endometrium.
For commercial and industrial production of citric acid, which one of the following microbes is used?
Select the correct statement from the following biotechnological procedures:
If Meselson and Stahl’s experiment is continued for 80 minutes (till III generation), then what would be the ratio of DNA containing \( N^{15}/N^{15} : N^{15}/N^{14} : N^{14}/N^{14} \) in the medium?
The decrease in the T-Lymphocytes count in human blood will finally result in

A child with blood group A has father with blood group B and the mother with blood group AB. Choose the option that gives the correct genotypes of father, mother, and the child:

A child with blood group A has father with blood group B

Study the items of Column-I and those of Column-II:

Choose the option that correctly matches the items of Column-I with those of Column-II: