Biology 5 Marks Questions

i. The insertion of recombinant DNA within the coding sequence of enzyme a-galactosidase results in the inactivation of the
enzyme called insertional inactivation. The colonies do not produce a blue colour in the presence of chromogenic substrate
and are identified as recombinant colonies whereas non-recombinant colonies produce blue colour from the chromogenic
substrate, due to the presence of the activated enzyme.
ii. The method is referred as "insertional inactivation" because the enzyme a-galactosidase produced is inactivated due to insertion of alien DNA within the coding sequence of the enzyme, which acts as a selectable marker to differentiate recombinant colonies from non-recombinant one.

a. In the absence of an inducer - The repressor of the Lac-operon is synthesised from the i gene, The repressor protein binds to the operator region of the operon in absence of the inducer, and prevents RNA polymerase from transcribing the operon.
b. In the presence of an inducer, (lactose) the repressor is inactivated by interaction with the inducer, This allows RNA polymerase access to the promoter and transcription proceeds.

a. Microsporangium located in the anther lobe in an angiosperm.
Tapetum- nourishes the developing pollen grain
Epidermis, Endothecium, middle layers- protection and dehiscence (of microsporangium)
b. Structure of Pollen grain / male gemetophyte
i. Outer wall layer - Exine
ii. Inner wall layer - Intine
iii. Vegetative cell
iv. Generative cell

c. Function of each part of male gametophyte are
i. Exine and Intine Protection
ii. Vegetative cell reserve food material / formation of pollen tube
iii. Generative cell formation of two male gametes

Polymerase Chain Reaction (PCR) is a technique to obtaining multiple copies of a gene of interest in vitro. This technique amplifies DNA through a simple enzymatic reaction. This technique was developed by Kary Mullis in 1965. The basic requirements of a PCR are the following:
i. DNA template
ii. Primers
iii. Enzyme-Taq polymerase
Amplification of recombinant DNA gene is done using Polymerase Chain Reaction (PCR). It is carried out in the following steps:
i. Denaturation - The double-stranded DNA is denatured by applying high temperature of 95°C for 15 seconds. Each separated strand acts as a template.
ii. Annealing -Two sets of primers are added, which anneal to the 3'end of each separated strand.
iii. Extension - DNA polymerase extends the primers by adding nucleotides complementary to the template provided in the reaction. Taq polymerase is used in the reaction, which can tolerate heat. All these steps are repeated many times to get several copies of the desired DNA.

DNA fingerprinting is used in forensic.
Steps which are involved in DNA fingerprinting are as follows:
i. Isolation of DNA
ii. Digestion of DNA by restriction endonuclease enzyme
iii. Separation of DNA fragments, by electrophoresis
iv. Transferring of separated DNA fragments to synthetic membrane such as nitrocellulose or nylon.
v. Hybridization, using labelled VNTR probe.
vi. Detection of hybridized DNA fragments by autoradiography

The similarity between geitonogamy and xenogamy is that both pollinations take place by pollinating agencies, pollinating agencies transfer the pollen from anther of one flower to the receptive stigma of another plant in case of xenogamy and another flower of the same plant in geitonogamy.

The difference between the two is that in geitonogamy the pollen and stigma are genetically similar because they both belong to the same plant but in xenogamy, they are genetically different as they belong to different plants of same species. Geitonogamy is functionally cross-pollination but genetically self-pollination.

As cleistogamous flowers are the flowers which remain closed and never open, so in these flowers anther and stigma are in close association. So these flowers do not require pollinating agencies for pollination and thus produce assured seed set even in absence of pollinating agencies.