Genetics and Molecular Biology
Core concepts
Master Mendelian inheritance and its extensions: incomplete dominance, codominance, multiple alleles, epistasis, and sex-linked inheritance. Be fluent with linkage, recombination frequency as a map unit, and the difference between cis and trans arrangement. In molecular biology, know DNA structure, semiconservative replication (leading and lagging strands, Okazaki fragments, primase, helicase, topoisomerase, DNA polymerase), transcription (promoters, RNA polymerase, capping, polyadenylation, splicing), and translation (codons, tRNA, ribosome A, P, and E sites, initiation and termination factors). Understand the lac operon (inducible, negative control relieved by allolactose, positive control by CAP-cAMP) and the trp operon (repressible). Know mutation classes (missense, nonsense, frameshift, silent), repair mechanisms, and the central dogma's exceptions (reverse transcription).
Common traps
Do not confuse recombination frequency with physical distance at large values; mapping functions are needed beyond about 50 map units. Distinguish a mutation in the coding region from one in a promoter. Remember that the lac repressor binds the operator, not the promoter. Codon degeneracy means a silent mutation changes no amino acid. In dihybrid crosses, a 9:3:3:1 ratio assumes independent assortment; linked genes distort it.
Worked example
Rule of thumb: for a testcross, the two most frequent progeny classes are parental and the two rarest are double crossovers. Given parentals AB/ab and recombinant frequency 20%, the map distance is 20 centimorgans. Always check whether the question asks for frequency (a proportion) or distance (map units) before answering.