In maize the genes A for purple leaves dominant over a for g

In maize, the genes A for purple leaves (dominant over a for green leaves), b for salmon silk (recessive to B for yellow silk), and d for pigmy plant (recessive to D for normal size plant) are on chromosome 6, with map positions as shown: Hybrids from the cross Abd/Abd times aBD/aBD were testcrossed with abd/abd plants. Predict the phenotypes of the offspring and their frequencies assuming interference of 0.2.

Solution

Answer:

Interference= 1- Coefficient of Coincidence(COC)

COC = 1-Interference

COC= 1-0.2 = 0.8

Expected double cross over = (Recombination frequency between A & B) * (Recombination frequency between B & D)

= 0.1 * 0.2 = 0.02

COC= Observed double cross over / Expected double cross over

Observed double cross over= COC * Expected double cross over

= 0.8 * 0.02 = 0.016

0.016 = 1.6% = 2%

Gene order = Abd/aBD

Recombinants due to crossing over between A & b are = ABD & abd

The frequency between them is = 10-2 = 8%

ABD/abd (purple, yellow, normal)= 4%

abd/abd (purple, salmon, pigmy)= 4%

Recombinants due to crossing over between b &d are = AbD & aBd

The frequency between them is = 20-2 = 18%

AbD/abd (purple, salmon, normal)= 9%

aBd/abd (green, yellow, pigmy)= 9%

Double cross overs are ABd & abD.

ABd/abd (purple, yellow, pigmy)= 1%

abD/abd (green, salmon, normal)= 1%

Non recombinants ( Abd & aBD) = 100- (2+8+18) = 100-28= 72

Abd/abd (purple, salmon,pigmy)= 36%

aBD/abd (green, yellow, normal) = 36%