Genetics and Molecular Biology
What this domain tests
Genetics and Molecular Biology tests information flow from DNA to phenotype, inheritance patterns, mutation, and core molecular techniques. Questions may ask you to predict progeny ratios, interpret pedigrees, identify strand polarity, or choose the correct blot or PCR interpretation.
Core rules and concepts
- DNA is synthesized 5′→3′; the template is read 3′→5′.
- Transcription uses RNA polymerase and a promoter; translation uses ribosomes, mRNA, and tRNAs.
- Mendelian independent assortment applies to genes on different chromosomes or far apart on the same chromosome.
- Linkage reduces recombinant frequency; recombination frequency approximates map distance in centimorgans for small distances.
- Mutations include substitutions, insertions/deletions that can cause frameshifts, and chromosomal rearrangements.
- Hardy–Weinberg assumes no selection, no mutation, no migration, random mating, and a large population.
Worked example
Cross AaBb × AaBb with independent assortment. Probability of A_bb: P(A_) = 3/4; P(bb) = 1/4; product = 3/16. If the genes were linked, the 9:3:3:1 ratio would not hold, and parental types would exceed recombinants. Reasoning: each locus segregates independently, so multiply probabilities; linkage changes gamete frequencies.
Traps that cost marks
Do not write the coding strand sequence as the mRNA without replacing T with U. Do not assume a dominant allele is more common. Do not confuse genotype frequency with allele frequency. Do not call a silent mutation harmless without context: it can affect splicing or codon usage. In pedigrees, do not assume carriers are always affected.