GUJCET Biology: Genetics, Molecular Biology and Ecology
GUJCET Biology is the third subject for PCB candidates: 40 single-correct MCQs, 1 mark each, with 0.25 deducted for a wrong answer. The GSEB Class 12 syllabus is the source, and the paper mixes recall (names, hormones, enzymes) with reasoning (pedigrees, crosses, experimental design). High-yield blocks are reproduction, inheritance, molecular biology, human health, biotechnology and ecology. Read the stem for qualifiers such as not, except and main, because many distractors are true statements that do not answer the question.
Core rules
- Genetics: use the product rule for independent events; a test cross reveals genotype; the Mendelian 9:3:3:1 ratio assumes independent assortment.
- Molecular biology: replication is semi-conservative; transcription uses the template strand; translation reads mRNA 5′→3′; the lac operon is induced by allolactose and blocked by the repressor.
- Human reproduction: the LH surge triggers ovulation; the corpus luteum secretes progesterone; hCG maintains it in early pregnancy.
- Biotechnology: restriction enzymes cut palindromic sequences; PCR needs primers, dNTPs and thermostable Taq polymerase; Bt toxin is activated in the alkaline insect gut.
- Ecology: energy flow is unidirectional and about 10% transfers between trophic levels; population growth is exponential when resources are unlimited.
Worked example
In a dihybrid cross AaBb × AaBb, what fraction of offspring show dominant A and recessive b? Treat the genes independently. For A: Aa × Aa gives 3/4 dominant A_. For B: Bb × Bb gives 1/4 recessive bb. Multiply: 3/4 × 1/4 = 3/16. This is the “3” class of the 9:3:3:1 ratio. If the genes were linked, the fraction would change, so independence must be stated or implied.
Traps that cost marks
- Writing “the dominant allele is more common” - dominance is about expression, not frequency.
- Confusing the coding strand with the template strand.
- Mixing n and 2n in meiosis diagrams.
- Reversing the direction of energy flow in a food web.
- Naming a hormone without its source or target when the question asks for both.
- In biotechnology, forgetting that DNA polymerase extends from a primer, not from scratch.