Biology 5 Marks Questions

Selection of recombinants due to inactivation of antibiotics is a laborious process as it requires:
i. a vector with two antibiotic resistance marker.
ii. preparation of two kinds of media plate with one antibiotic each.
→ Transformed cells are first plated on that antibiotic plate which has not been insertional inactivated (ampicillin) and incubated overnight for growth of transformants. For the selection of recombinants, these transformants are Replica plated on second antibiotic (tetracycline) plate (which got inactivated due to insertion of a gene). Non-recombinants grow on both the plates (one carrying ampicillin and the other carrying tetracycline) while recombinants will grow only on ampicillin plate.
→ This entire exercise is laborious and takes more time (two overnight incubation) as well. However, if we choose the second option (insertional inactivation of a marker that produces colour in the presence of a chromogenic compound), we can distinguish between the recombinants and nonsubstrate recombinants on a single medium plate (containing one antibiotic and the chromogenic compound) after overnight growth.

i. The three method of pollen transfer in plant are
1. Autogamy
2. Geitonogamy
3. Xenogamy
ii. 1. Water lily: achieve successfully pollination by insects/wind.
2. Vallisneria: Female flowers on long stalks reach water surface male flowers or pollen released on water and carried by water current to female flowers to achieve pollination.
iii. Genetic: Self-incompatibility/prevents self-pollen (same flower or other flowers of same plant) from fertilizing the ovules by inhibiting pollen germination, pollen tube growth in pistil.
Physiological: Pollen release and stigma receptivity are not synchronized, either pollen matures earlier and stigma later or pollen matures later than stigma.

i. In the above bacterial cell, i.e. A is plasmid B is chromosomal DNA. The plasmid is used as a vector in rDNA technology.
ii. If the enzyme EcoRl acts on both linear DNA and plasmid DNA, each having three recognition sites, the restriction enzyme will generate 3 fragments from plasmid DNA (as it is circular) and 4 fragments from linear DNA.

A functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter is called an operon. An operon is generally transcribed into polycistronic mRNA. A single mRNA which codes for more than one protein is called polycistronic mRNA. An operon is made up of 3 basic DNA components:
i. Promoter: A nucleotide sequence that enables a gene to be transcribed is called a promoter. It is recognized by RNA polymerase, which then initiates transcription.
ii. Operator: A segment of DNA to which a repressor binds is called the operator.
iii. Structural genes: The genes that are co-regulated by the operon are called structural genes. Inducible Operon: When the operon is regulated by an inducer, it is called an inducible operon. An inducer can switch on or off the operon. Lac operon is an example of an inducible operon. Lactose is a substrate of enzyme beta-galactosidase and is the inducer of the lac operon.


The given diagram shows the working of the lac operon. In the absence of an inducer, the repressor binds to the operator region and prevents transcription.
In the presence of an inducer, repressor becomes inactive. This allows transcription in the operator region which results in the release of mRNA. Subsequently, mRNA promotes translation and protein synthesis is accomplished