BIN300 W1- genetic distances

genetic distances

number of cross-overs between loci

recombinations vs cross-overs

Think of recombination as the entire process of recipe mixing for new dishes. A crossover is like physically swapping ingredients (e.g., exchanging spices between two recipes) — a specific part of the process.

genetic distance d

average number crossover per chromsome segment

morgan

genetic distance where on average 1 crossover occurs

recombination fraction Ɵ

fraction of times of uneven number of crossovers

recombination → are 2 loci inherited together or not?

Max Ɵ = 0.5

physical distances between loci

number of kbase pairs (nucleotides

recombination distance Ɵ

probability of uneven number of cross-overs (max. Ɵ = 1/2)

genetic distance in cMorgan

1 cM

1 cM is on average 1 crossover/100 meiosis

mapping function in relation to genetic distance

Ɵ = f(d)

Ɵ=d (Morgan mapping function)

generally non-linear function

describes relationship between d and Ɵ

Morgan and Haldane mapping function graph

haldane mapping function

assumes independent cross over probs

• no interference

Ɵ=1/2(1-exp(-2d))

d=1/2ln(1-2Ɵ)

addition rule for 3 loci A_B_C

dAC = dAB + dBC

ƟAC=ƟAB+ƟBC-2ƟABƟBC

Kosambi mapping function

assumes interference

• crossover at locus X affects prob of recombination at locus X+d

  • interference decreases with distance