The Q and R loci are 25 mu apart If a plant of genotype QRqr

The Q and R loci are 25 m.u. apart. If a plant of genotype QR/qr is selfed, what percentage of the progeny will be qr in phenotype? (i.e. display both recessive alleles) Assume equal crossing over in the sexes of this plant. 64.06% 10.94% 14.06% 56.25% 15.63%

Solution

Answer: c.14.06 %

Explaination: As per the given condition the recombination frequency is 25% -It means recombinant progeny is 25% and 75% is parental progeny (QR/qr). If this plant of genotype QR/qr is selfed (QR/qr x QR/qr), will give the following results:

Gametes proportion is calculated as:

QR (parental) : 1/2 (1 – 0.25) = 0.375 OR 37.5%

qr (parental) : 1/2 (1 – 0.25) = 0.375 OR 37.5%

Qr (recombinant): 1/2 (0.25) = 0.125 OR 12.5%

qR (recombinant) : 1/2 (0.25) = 0.125 OR 12.5%

Genotype proportion after self cross is calculated as:

QR/QR = 0.375 x 0.375 = 0.1406

qr/qr = 0.375 x 0.375 = 0.1406

qr/QR = 0.375 x 0.375 = 0.1406

QR/qr = 0.375 x 0.375 = 0.1406

qR/QR = 0.125 x 0.375 = 0.0469

Qr/QR = 0.125 x 0.375 = 0.0469

QR/qR = 0.375 x 0.125 = 0.0469

QR/Qr = 0.375 x 0.125 = 0.0469

Qr/qr = 0.125 x 0.125 = 0.0156

qR/qR = 0.125 x 0.125 = 0.0156

Qr/qr = 0.125 x 0.375 = 0.0469

qR/qr = 0.125 x 0.375 = 0.0469

Qr/qR = 0.125 x  0.125 = 0.0156

Qr/qr = 0.125 x 0.375 = 0.0469

qR/qr = 0.125 x 0.375 = 0.0469

Qr/Qr = 0.125 x  0.125 = 0.0156

Phenotype proportion is calculated as:

QR : (0.6094) = 60.94 %

Qr : (0.125)= 12.5%

qR : (0.125) = 12.5%

qr : (0.1406) = 0.1406 OR 14.06 %