Short Answer Type(a) How do organic farmers control pests ? Give two examples.
(b) State the difference in their approach from that of conventional pest control methods.
(a) Name the selectable markers in the cloning vector pBR322 ? Mention the role they play.
(b) Why is the coding sequence of an enzyme 
-galactosidase a preferred selectable marker in comparison to the ones named above ?
(a) Why must a cell be made 'competent' in biotechnology experiments ? How does
calcium ion help in doing so ?
(b) State the role of 'biolistic gun' in biotechnology experiments.
Long Answer TypeA large number of married couples the world over are childless. It is shocking to know that in India the female partner is often blamed for the couple being childless.
(a) Why in your opinion the female partner is often blamed for such situations in India ? Mention any two values that you as a biology student can promote to check this social evil.
(b) State any two reasons responsible for the cause of infertility.
(c) Suggest a technique that can help the couple to have a child where the problem is with the male partner.
(a) What is polygenic inheritance ? Explain with the help of a suitable example.
(b) How are pleiotropy and Mendelian pattern of inheritance different from polygenic pattern of inheritance ?
(a) Polygenic inheritance is an inheritance pattern controlled by three or more genes (multiple genes) and the graded phenotypes are due to the additive or cumulative effect of all the different genes of the trait. An example of human skin colour to understand the phenomenon of polygenic inheritance. Skin colour in humans is caused by a pigment called melanin. The quantity of melanin is due to three pairs of polygenes (A, B and C).
Black or very dark is represented by (AA BB CC) and
White or very light is represented by (aa bb cc).
Individuals with the genetic constitution (Aa Bb Cc) have an intermediate colour often called mulatto .
A total of eight allele combinations is possible in the gamets forming 27 distinct genotypes distributed into 7 phenotypes, i.e. very dark, dark, fairly dark, intermediate,fairly light and very light.
(b) In Mendelian inheritance, only one gene controls one trait. Ogenegen may have two different forms of an allele. However, in Polygenic there is more than one gene controlling one trait.
For example, the gene of tallness in the case of Mendelian character has two form of the allele, both of which affect the height of the plant.
In the case of skin colour three genes A, B and C control the skin colour.
In Pleiotropy one gene affects more than one phenotype or trait. However in polygenic inheritance more than one gene controls or affects one phenotype.
In case of the amino acid tyrosine. It is needed for general protein synthesis, and it is also a precursor for several neurotransmitters (e.g., dopamine, norepinephrine), the hormone thyroxine, and the pigment melanin. Thus, mutations in any one of the genes that affect tyrosine synthesis or metabolism may affect multiple body systems. These and other instances in which a single gene affects multiple systems and therefore has widespread phenotypic effects.
(a) Name the stage in the cell cycle where DNA replication occurs.
(b) Explain the mechanism of DNA replication. Highlight the role of enzymes in the process.
(c) Why is DNA replication said to be semiconservative ?
(a) Name the two growth models that represent populations growth and draw the respective growth curves they represent.
(b) State the basis for the difference in the shape of these curves.
(c) Which one of the curves represent the human population growth at present ? Do you think such a curve is sustainable ? Give reason in support of your answer.
(a) Taking an example of a small pond explain how the four components of an ecosystem function as a unit.
(b) Name the type of food chain that exists in a pond.
Switch
