Biology MCQs with Answers and Explanations

Genetically modified crops containing the Bt (Bacillus thuringiensis) toxin gene are resistant to:

A. Herbicides
B. Insect pests
C. Drought
D. Viral infection

Explanation:
The Bt gene encodes an insecticidal protein. Plants expressing Bt produce a toxin that targets specific insect pests, providing built-in insect resistance.

Golden rice has been genetically engineered to produce which nutrient precursor?

A. Vitamin C
B. Beta-carotene (provitamin A)
C. Vitamin E
D. Folic acid

Explanation:
Golden rice contains genes for beta-carotene biosynthesis, which is a precursor of vitamin A, to help alleviate vitamin A deficiency.

Why is fetal bovine serum commonly added to cell culture media?

A. To buffer the pH
B. To provide growth factors and nutrients
C. To increase osmolarity
D. To act as an antibiotic

Explanation:
Fetal bovine serum supplies a mix of growth factors, hormones, and nutrients that support cell growth and viability in culture.

What distinguishes reverse transcription PCR (RT-PCR) from standard PCR?

A. Use of DNA ligase
B. Amplification of RNA by first creating complementary DNA
C. Higher temperature cycles
D. Use of radioactive nucleotides

Explanation:
RT-PCR involves reverse transcription of RNA into cDNA before PCR, enabling amplification of RNA targets.

Enzyme-linked immunosorbent assay (ELISA) is primarily used to:

A. Measure DNA concentration
B. Detect specific proteins or antibodies by an enzyme-mediated color change
C. Visualize chromosomes under a microscope
D. Amplify RNA

Explanation:
ELISA employs enzyme-linked antibodies. When the target antigen or antibody is present, a substrate is converted to a colored product, indicating a positive result.

Which method uses an electrical pulse to introduce DNA into cells?

A. Microinjection
B. Electroporation
C. Lipofection
D. Ultracentrifugation

Explanation:
Electroporation applies a brief high-voltage pulse to permeabilize cell membranes, transiently allowing DNA uptake.

In molecular cloning with a plasmid containing the lacZ α-fragment and a multiple cloning site, what color do colonies appear on X-gal/IPTG plates if the plasmid has an inserted DNA fragment?

A. Blue
B. White
C. Red
D. Green

Explanation:
Insertion disrupts lacZ α-peptide, so β-galactosidase is not produced. Colonies remain white (no cleavage of X-gal), indicating successful insertion.

Which of the following techniques compares short tandem repeat (STR) regions among individuals for identification?

A. Western blot
B. DNA microarray
C. DNA fingerprinting
D. Northern blot

Explanation:
DNA fingerprinting analyzes highly polymorphic regions, especially STRs, to distinguish individuals (used in forensics and paternity testing).

Down syndrome (trisomy 21) results in how many total chromosomes in a karyotype?

A. 45
B. 46
C. 47
D. 48

Explanation:
Down syndrome is caused by an extra copy of chromosome 21. Humans normally have 46 chromosomes; trisomy adds one extra, making 47.

In genomic imprinting, the expression of a gene depends on its parental origin. For example, only the paternally inherited allele of a certain gene is expressed. This is known as:

A. Epigenetic modification
B. Loss of heterozygosity
C. Imprinting
D. Mendelian inheritance

Explanation:
Genomic imprinting is an epigenetic phenomenon where only one allele (maternal or paternal) is expressed, depending on the parent of origin, while the other is silenced.