Subject

Biology

Class

CBSE Class 12

Pre Boards

Practice to excel and get familiar with the paper pattern and the type of questions. Check you answers with answer keys provided.

Sample Papers

Download the PDF Sample Papers Free for off line practice and view the Solutions online.
Advertisement

 Multiple Choice QuestionsShort Answer Type

Advertisement

11.

With the help of an algebraic equation, how did Hardy-Weinberg explain that in a given population the frequency of occurrence of alleles of a gene is supposed to remain the same through generations?


In a given population one can find out the frequency of occurrence of alleles of a gene or a locus. This frequency is supposed to remain fixed and even remain the same through generations. Hardy-Weinberg the principle stated it using algebraic equations.

This principle says that allele frequencies in a population are stable and is constant from generation to generation. The gene pool (total genes and their alleles in a population) remains a constant. this is called genetic equilibrium.

Sum total of all the allelic frequencies is 1. Individual frequencies, for example, can be named p, q, etc. In a diploid, p and q represent the frequency of allele A and allele a. The frequency of AA individuals in a population is simply p2. This is simply stated in another way, i.e., the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities,i.e., p2. Similarly of aa is q2, of Aa 2pq. Hence, p2 + 2pq + q2 = 1. This is a binomial expansion of (p + q)2.

When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change. Disturbance in genetic equilibrium, or Hardy-Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.


Advertisement
12.

Although a prokaryotic cell has no defined nucleus, yet DNA is not scattered throughout the cell. Explain.


13.

Differentiate between analogous and homologous structures.


14.

Select and write analogous structures from the list given below:

(i) Wings of butterfly and birds

(ii) Vertebrate hearts

(ii) Tendrils of bougainvillaea and Cucurbita

(iv) Tubers of sweet potato and potato


Advertisement
15.

How has the use of Agrobacterium as vectors helped in controlling Meloidogyne incognita infestation in tobacco plants? Explain in the correct sequence.


16.

“India has greater ecosystem diversity than Norway.” Do you agree with the statement? Give reasons in support of your answer.


17.

Write the difference between genetic biodiversity and species biodiversity that exists at all the levels of biological organisation.


18.

Explain the mechanism of ‘sex determination’ in birds. How does it differ from that of human beings?


Advertisement
19.

Explain outbreeding, outcrossing and cross-breeding practices in animal husbandry.


20.

Organic farmers prefer the biological control of diseases and pests of the use of chemicals for the same purpose. Justify.


Advertisement