Probability Of Gametes and Crossovers

Probability of two gametes uniting to form a zygote is the probability of one type of gamete multiplied by the probability of the second type of gametic.

P(AABB zygote) = P(AB) P(AB)

For coupling phase linkage this is:

For repulsion phase linkage this is:

Probability of a crossover event = 2p.
Each single crossover event results in 50% recombinant gametes and 50% parental type gametes.

Precent recombinant gametes expected
= P(crossover event) x 50% = 2p(50%) = p

Example:

Two loci are linked, p = 0.2
Percent recombinant gametes expected = 2p(50%)
Percent recombinant gametes expected = 2(0.2)(0.5)
Percent recombinant gametes expected = 0.2

Say we have coupling phase linkage and then Ab and aB are recombinant types of gametes with p = 0.2
Prob.(Ab) = p/2 = 0.1
Prob.(aB) = p/2 = 0.1
Prob. (parental type) = 0.2 = 20% because p = 0.2

Precent recombinant gametes expected x 2
= Prob. (crossover event)
p x 2 = 2p = Prob.(crossover event)

Example:

Two loci are on the same chromosome, but segregate independently and p =0.5

p x 2 = 0.5(2) = 1
On average there is one crossover event per meiotic event when p = 0.5