Biology Test 331

Option (b) is the correct answer as a palindromic DNA sequence is a DNA sequence of base pairs that reads same on the two strands when orientation of reading is kept the same. Out of the four options, option (b) is the only palindromic sequence.

5'GAATTC3'

3'CTTAAG5'

The assertion accurately states that in pea plants, the allele for yellow seed color is dominant over the allele for green seed color. The reason is also true and correctly explains the assertion because plants with yellow seeds can have either a homozygous dominant (YY) or heterozygous (Yy) genotype, which is how dominance works in Mendelian genetics.

Option (d) is the correct answer. Cloning vectors are the carriers of the desired gene in the host cell.

The features desirable in a cloning vector are:-

• Presence of origin of replication

• Presence of marker genes

• Presence of very few, preferably single recognition site for the commonly used restriction enzymes

The assertion is true because a man affected by hemophilia will pass his affected X chromosome to all of his daughters, making them carriers of the disease. The reason is also true and provides the correct explanation because hemophilia is indeed a sex-linked recessive disorder carried on the X chromosome, and males pass their single X chromosome to all their daughters.

The first step in the polymerase chain reaction is denaturation during which strands of dsDNA separate. This requires temperature around 94°C.

This is followed by annealing in which primers anneal to 3' end of template DNA strand.

Annealing is followed by extension in which Taq polymerase adds nucleotides to 3'OH end of primers.

RNA polymerase is involved in the process of transcription, not DNA replication. It synthesizes RNA from the DNA template.

pBR322 is a commonly used cloning vector. When the gene for β-galactoside is inserted in the ampicillin resistance gene by using Pst I, the recombinant E.coli will lose ampicillin resistance due to insertional inactivation of the antibiotic resistance gene.

The host (recombinant) cell will produce β-galactoside which is not a novel protein nor does it have dual ability.

The transformed cells cannot resist ampicillin as they have lost ampicillin resistance.

A recombinant E. coli is produced and the host cell will not undergo lysis due to insertion of β-galactoside gene.

Insertion or deletion of a nucleotide causes a frameshift mutation, altering the reading frame of the genetic message and potentially changing every amino acid that follows the point of mutation, often leading to a nonfunctional protein.

• Option (c) is correct. High temperature about 94°C is required for the process of denaturation which is the first step of PCR.

• Ligation of DNA fragments is performed with the help of an enzyme called DNA ligase.

• Annealing is performed at 50°-60°C which is the second step that can get affected.

• Addition of nucleotides to the primer, synthesizing a new DNA strand using only the template sequences with the help of enzyme DNA polymerase is called primer extension/ polymerisation.

The lac operon is regulated by a repressor protein that is bound to the operator region of the operon, inhibiting transcription in the absence of lactose. When lactose is present, it acts as an inducer by binding to the repressor and inactivating it, allowing transcription to proceed.