All Free Biology MCQs with Answers

• A. We can cut DNA at specific sites by endonucleases like DNase I.
• B. Restriction endonucleases purified from bacteria can be used in vitro.
• C. The phenomenon of transduction in bacteria is well understood.
• D. We can see DNA by electron microscope.

Explanation: DNA restriction endonuclease are an important class of restriction exonucleases, class II, which cut double­stranded DNA molecules only at sites characterized by a specific nucleotide sequence. Restriction enzymes are isolated from bacterial cells, and are tools for molecular biologists. Several hundred restriction enzymes are now known, each with a specific sequence requirement dictating where it will cut DNA. Some, such as Hind III, make staggered cuts leaving 'sticky ends', three nucleotides long protruding on one strand from each severed terminus; others make clean cuts in both strands at the same place and thus generate 'blunt ends'. Digesting DNA with a restriction enzyme therefore creates a characteristic set of fragments, which can be isolated by electrophoresis and subsequently analyzed.

• A. They can cut DNA at specific base sequence.
• B. They are nucleases that cut DNA at variable sites.
• C. They can degrade harmful proteins.
• D. They can join different DNA fragments.

Explanation: DNA restriction endonuclease are important class of restriction exonucleases, class II, which cut double­stranded DNA molecules only at sites characterized by a specific nucleotide sequence. Restriction enzymes are isolated from bacterial cells, and are tools for molecular biologists. Several hundred restriction enzymes are now known, each with a specific sequence requirement dictating where it will cut DNA. Some, such as Hind III, make staggered cuts leaving 'sticky ends', three nucleotides long protruding on one strand from each severed terminus; others make clean cuts in both strands at the same place and thus generate 'blunt ends'. Digesting DNA with a restriction enzyme therefore creates a characteristic set of fragments, which can be isolated by electrophoresis and subsequently analysed.

• A. Mitochondria
• B. Plasmids
• C. Golgi bodies
• D. Lysosomes

Explanation: Plasmids are an extrachromosomal genetic element found in many bacteria and in a few eukaryotic cells. Plasmids are closed circles of double­ stranded DNA, ranging in size from one to 200 kilobases. They frequently carry genes conferring antibiotic resistance. Plasmids are becoming important tools for genetic engineering since they have the ability to replicate and migrate to daughter cells. Plasmids are widely used as carriers of cloned genes, as for example the E.coli plasmid pBR322. When plasmids are used as cloning vectors and carry a novel DNA sequence they are referred to as chimeric plasmids.

• A. Mating of unrelated individuals of same breed.
• B. Mating of individuals of different breed
• C. Mating of individuals of different species.
• D. Mating of related individuals of same breed.

Explanation: When breeding is between animals of the same breed for 4­-6 generation, it is called inbreeding. Inbreeding, as a rule, increases homozygosity. Thus, inbreeding is necessary if we want to obtain a pure line in any animal.

• A. Animals within same breed without having common ancestors
• B. Two different related species
• C. Superior males and females of different breeds.
• D. More closely related individuals within same breed for 4-6 generations.

Explanation: In interspecific hybridization, a species is mated with a different related species of the same genus. Interspecific hybrids are generally difficult to produce, but they are important in plant breeding, particularly in breeding for disease resistance. This is also called intrageneric hybridization.

• A. Mystus
• B. Mangur
• C. Mrigala
• D. Mackerel

Explanation: Mackerel is a marine fish, rich in omega­-3­ fatty acids. Mystus, Mangur and Mrigala are freshwater fishes.

• A. strip farming
• B. shifting agriculture
• C. ley farming
• D. contour farming.

Explanation: Ley farming is an agricultural system where the field is alternately seeded for grain and left fallow for growing hay or used for pasture. During the fallow/pasture period the soil is filled with roots of grasses and other plants. New ploughing mixes them in the soil and also increases the amount of nitrogen in the soil especially when legume forage are used. It also protects soil from erosion by maintaining constant soil coverage.

• A. is useful in overcoming inbreeding depression
• B. exposes harmful recessive genes that are eliminated by selection
• C. helps in accumulation of superior genes
• D. is useful in producing purelines of animals.

Explanation: Outbreeding is the breeding of unrelated animals, which may be between individuals of the same breed (but having no common ancestors), or between different breeds (cross breeding) or different species (inter specific hybridisation). Outbreeding is an important strategy of animal husbandry as it helps to overcome inbreeding depression.

• A. protoplast fusion
• B. embryo rescue
• C. somatic hybridisation
• D. somatic embryogenesis.

Explanation: Micropropagation is the latest method of obtaining a large number of plantlets from plant tissue culture. It is called micropropagation because of the minute size of the propagules. It involves repeated subculture of the explant by changing the medium so as to form a large number of plantlets from that single explant. Somatic embryogenesis i.e., developing embryos from somatic cells is one of the techniques of micropropagation.

• A. I AA and kinetin
• B. IAA and gibberellins
• C. Sodium chloride and potassium chloride
• D. Polyethylene glycol and sodium nitrate

Explanation: When a hybrid is produced by the fusion of somatic cells of two varieties or species, it is known as a somatic hybrid. The process of producing somatic hybrids is called somatic hybridization. First, the cell wall of the plant cells are removed then the protoplasts of the two cells are brought in contact and made to fuse by means of electrofusion or chemicals like polyethylene glycol (PEG) and sodium nitrate. The fused protoplasts soon develop their own walls and are called somatic hybrids.