Data is given below for a three-point testcross for three genes (M. N and O) on

Question

Data is given below for a three-point testcross for three genes (M. N and O) on the same chromosome: M?nNnOo female x mmnnoo male. The capital-lettered alleles are dominant. Genotype of female gamete # progeny 1) Which of the following correctly describes the order of these three genes on the chromosome? A) M-N-O B) M-O-N C) N-M-O D) not enough information 2) Which of the following is the correct distance between genes M and N, in map units? A) 15.0 B) 17.6 C) 21.3 D) 23.9 E) 41.5 3) Which of the following is the correct distance between genes N and O, in map units? A) 15.0 B) 17.6 C) 21.3 D) 23.9 E) 41.5 4) What is the level of interference for the double crossover event in this testcross? A) 0.62 B) 0.645 C) 0.38 D) 0.184 E) 0.55

Explanation / Answer

Recombinant between M and N

= 16+123+107+24= 270

Recombinant frequency = 270/1534 = 17.60%, so distance between them would be 17.60 map unit

Recombinant between N and O

= 123+151+ 107+175 = 556

Recombinant frequency = 556/1534 = 36.24%, so distance between them would be 36.24 map unit

Recombinant between M and O

= 16+151+175+24 = 366

Recombinant frequency = 366/1534 = 23.85%, so distance between them would be 23.85 map unit

Map

N      17.60     M   23.85                  O   

Coefficient of coincidence

Number of double cross over = 24+16 = 40

The expected occurrence of double cross over is 0.1760

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