Microbial genetics formulas
Microbial genetics, gene transfer and transposable elements. 5 formulas for GATE BT Genetics, Cell and Molecular Biology, each with when to use it. Each is explained in the topic notes.
IAE Academy: Microbial genetics, gene transfer and transposable elements formulas (GATE BT)
All 5 Microbial genetics formulas
INTERRUPTED-MATING TIME-OF-ENTRY DISTANCE
t₁ and t₂ are the times of entry (minutes after mixing) of two markers transferred by the same Hfr strain in the same direction. Distances from different Hfr strains are compared only after aligning each strain's order on the circular map.
COTRANSDUCTION FREQUENCY (DEFINITION)
C is a fraction (multiply by 100 for a percentage). Select for one donor marker, then score the unselected marker. Cotransformation frequency is defined the same way among transformants.
WU FORMULA (GENERALIZED TRANSDUCTION)
C is the cotransduction frequency (a fraction), d the distance between the two markers, and L the length of the packaged fragment. d and L must be in the same unit, either kb or map minutes; for P1, L is about 2 min of the E. coli map. The formula assumes the fragment ends fall at random and holds for d < L. C falls to 0 as d approaches L and is taken as 0 for d ≥ L.
DISTANCE FROM COTRANSDUCTION FREQUENCY (WU FORMULA REARRANGED)
Use this to find d from a measured cotransduction frequency C (as a fraction, not a percentage). The same conditions as the Wu formula apply.
RECOMBINATION FREQUENCY AND MAP UNITS
RF is expressed as a percentage, and 1% RF = 1 map unit (cM). It applies to crosses scored for recombinant and parental classes (including phage crosses). This scale cannot be converted directly into the minutes of an interrupted-mating map.
Where this was asked: 2019 (1), 2025 (1). See the 2 previous-year questions on Microbial genetics. This shows what was asked, not what will be asked.