Biology: Genetics, Molecular Biology and Ecology
Biology in Thanawiya Amma tests genetics, molecular biology, evolution, ecology, and human physiology including immunity. Questions often ask for a cross, a molecular sequence, or an interpretation of data.
Core rules
- Mendel's law of segregation: alleles separate during gamete formation; a monohybrid cross Aa × Aa gives 1 AA : 2 Aa : 1 aa, or 3 : 1 phenotypes when A is completely dominant.
- A test cross uses a homozygous recessive partner to reveal an unknown genotype.
- DNA replication is semi-conservative; transcription makes mRNA from the template strand; translation reads mRNA codons 5′ to 3′.
- Evolution acts on variation; natural selection changes allele frequencies.
- Ecology: energy flows through trophic levels and is lost as heat; nutrients cycle.
Worked example
Cross Aa × Aa. Each parent produces A and a gametes in equal proportion. A Punnett square gives AA, Aa, Aa, aa: genotypic ratio 1:2:1 and phenotypic ratio 3:1 if A is completely dominant. If the traits show incomplete dominance, the phenotypic ratio becomes 1:2:1 because heterozygotes have an intermediate phenotype.
Traps
- Confusing codominance with incomplete dominance.
- Assuming independent assortment for linked genes.
- Reading the mRNA strand in the wrong direction.
- Forgetting that energy is lost between trophic levels.
- Treating a change in an individual as evolution rather than a change in population allele frequency.