Biology - Cell Biology and Genetics
Biology - Cell Biology and Genetics covers organelles, membrane transport, enzymes, the cell cycle, mitosis and meiosis, DNA, and Mendelian inheritance. Expect diagram-free descriptions and probability questions.
Core rules
- Prokaryotes lack membrane-bound organelles; eukaryotes compartmentalize reactions.
- Diffusion is passive down a gradient; osmosis is water movement across a selectively permeable membrane; active transport uses ATP.
- Enzymes lower activation energy and are denatured by extreme pH or heat.
- Mitosis produces genetically identical diploid cells; meiosis produces four haploid gametes with recombination.
- Monohybrid cross Aa × Aa gives genotype ratio 1 AA : 2 Aa : 1 aa and phenotype ratio 3 dominant : 1 recessive.
Worked example
Two heterozygous tall pea plants (Tt) are crossed. Predict the offspring. Set up gametes: each parent produces T and t with equal probability. A Punnett square gives TT, Tt, Tt, tt. Genotypes: 1 TT : 2 Tt : 1 tt. Phenotypes: 3 tall : 1 short, because T is dominant. The probability that a randomly chosen offspring is short is 1/4, or 25%. The probability it is heterozygous is 2/4 = 50%.
Traps
- Confusing genotype ratio with phenotype ratio.
- Treating “dominant” as “more common”; it only masks the recessive allele.
- Forgetting that meiosis halves chromosome number before fertilization.
- Assuming linked genes assort independently; linkage reduces recombinant frequency.
- Mixing up codominance with incomplete dominance.